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Traveltimes for global earthquake location and phase identification
Abstract
Over the last three years, a major international effort has been made by the Sub-Commission on Earthquake Algorithms of the International Association of Seismology and the Physics of the Earth's Interior (IASPEI) to generate new global traveltime tables for seismic phases to update the tables of Jeffreys & Bullen (1940). The new tables are specifically designed for convenient computational use, with high-accuracy interpolation in both depth and range. The new iasp91 traveltime tables are derived from a radially stratified velocity model which has been constructed so that the times for the major seismic phases are consistent with the reported times for events in the catalogue of the International Seismological Centre (ISC) for the period 1964–1987. The baseline for the P-wave traveltimes in the iasp91 model has been adjusted to provide only a small bias in origin time for well-constrained events at the main nuclear testing sites around the world.
For P-waves at teleseismic distances, the new tables are about 0.7s slower than the 1968 P-tables (Herrin 1968) and on average about 1.8–1.9 s faster than the Jeffreys & Bullen (1940) tables. For S-waves the teleseismic times lie between those of the JB tables and the results of Randall (1971).
Because the times for all phases are derived from the same velocity model, there is complete consistency between the traveltimes for different phases at different focal depths. The calculation scheme adopted for the new iasp91 tables is that proposed by Buland & Chapman (1983). Tables of delay time as a function of slowness are stored for each traveltime branch, and interpolated using a specially designed tau spline which takes care of square-root singularities in the derivative of the traveltime curve at certain critical slownesses. With this representation, once the source depth is specified, it is straightforward to find the traveltime explicitly for a given epicentral distance. The computational cost is no higher than a conventional look-up table, but there is increased accuracy in constructing the traveltimes for a source at arbitrary depth. A further advantage over standard tables is that exactly the same procedure can be used for each phase. For a given source depth, it is therefore possible to generate very rapidly a comprehensive list of traveltimes and associated derivatives for the main seismic phases which could be observed at a given epicentral distance.
... The first part of this study was to analyse all the waveforms using the Geotool software (2016) from the CTBTO to determine the origin time, epicentre, focal depth, and magnitude of the Moiyabana earthquake. Geotool used the International Data Centre's (IDC) default model (i.e. the 1-D IASP91 model (Kennett & Engdahl, 1991)). A total number of 41 broadband seismic stations (Fig. 2) used in this analysis ranged in epicentral distance from 0.72°to 73.96°. ...
... However, the 41 stations used in this analysis enclosed the epicentral region such that their distribution achieved a very good azimuthal coverage with a station gap of 89° (Table 3). The relocation of the mainshock of the Moiyabana earthquake using IASP91 model (Kennett & Engdahl, 1991) with the Geotool software (2016) indicates that it occurred at 22.645°S and 25.220°E. The earthquake epicentre latitude and longitude mislocation errors are approximately ± 4.09 km and ± 1.74 km, respectively. ...
... However, it should be noted that there is no clear consensus on the westward extension of the Limpopo belt as it varies depending on authors. The epicentral locations Table 3 A summary of the Moiyabana earthquake source parameter solution as well as phase data generated using the IASP91 model (Kennett & Engdahl, 1991) Results of epicentral locations, magnitudes, and origin times of this event from the different seismological agencies agree to within * 12 km with those from the current study as shown in Table 5. These results place the event within the Limpopo belt, while the SFS mislocates it to the Kweneng region or district which is * 131 km away, south of the other solutions (Table 5 and Fig. 4). ...
On the 3rd April 2017 a widely felt Moiyabana earthquake shook Botswana and the rest of southern Africa. Previous Moiyabana earthquake locations used mainly teleseismic or regional seismograms; and/or non-seismic methods which include Synthetic Aperture Radar (InSAR), and magnetotelluric (MT). These results did not agree, as evidenced by the depth of the earthquake that ranged from zero to 30 km (i.e. indicating either a man-made event or a natural event); thus motivating us to re-assess the location parameters. Unfiltered seismic waveform data from the recent project of the Network of Autonomously Recording Seismographs (NARS) in Botswana was complimented with stations from the International Monitoring System (IMS) to relocate the event. Relocated parameters are origin time, epicentre, focal depth, and magnitude. Geotool software from the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), and the Regional Seismic Travel Time model (RSTT) were used to process vertical components waveforms from 9 NARS and 32 IMS stations. Geotool results are: earthquake epicentre (22.645 °S: 25.220 °E); origin time of 17:40:16.9 (UTC); hypocentral depth range of 22 to 24 km; body magnitude (mb) and local magnitude (ml) of 6.3 ± 0.6 and 6.0 ± 0.8, respectively. RSTT results are: earthquake epicentre (22.667 °S: 25.257 °E); origin time of 17:40:16.95 (UTC); hypocentral depth of 25 km; and mb of 6.65 ± 0.03. The seismological location parameters from Geotool and RSTT, agree very well within experimental uncertainties with the non-seismic geophysical methods.
... The mainshock location, origin time, and theoretical P and pP wave arrival times controlled the rupture imaging, allowing a reference frame to merge multiple array backprojections. P and pP wave arrival times were predicted based on the IASP91 velocity model (Kennett & Engdahl, 1991). For P waves, static corrections were determined by measuring the relative time shifts of first arrivals with the adaptive stacking method of Rawlinson and Kennett (2004). ...
... We combined P and pP backprojections for earthquakes deeper than 40 km and only if the theoretical pP wave amplitude reached a minimum of 40% of the direct P wave amplitude; see Section 3.2 for synthetic tests and extended discussion on the radiation pattern. This provides a minimum separation time between P and pP wave arrivals of ∼11 s (depth ≥40 km; arrays at epicentral distances of 30-100°) in the IASP91 Model (Kennett & Engdahl, 1991). The ≥40 km depth threshold is additionally aimed to mitigate the impact of depth phases in the back-projection, as observed for intermediate-depth (40-100 km) earthquakes (e.g., Zeng et al., 2020). ...
... Events labeled with a black bullet indicate that a secondary rupture pattern was obtained over a predefined grid and included in the rupture parameter estimates. The vertical red bars in the rupture speed panel show the expected shear wave speed (V S ) at the hypocentral depth in the IASP91 velocity model (Kennett & Engdahl, 1991). Rupture speeds in the range 95-105%V S and >105%V S define "likely' and "strongly" supershear earthquakes, respectively. ...
Teleseismic back‐projection imaging has emerged as a powerful tool for understanding the rupture propagation of large earthquakes. However, its application often suffers from artifacts related to the receiver array geometry. We developed a teleseismic back‐projection technique that can accommodate data from multiple arrays. Combined processing of P and pP waveforms may further improve the resolution. The method is suitable for defining arrays ad‐hoc to achieve a good azimuthal distribution for most earthquakes. We present a catalog of short‐period rupture histories (0.5–2.0 Hz) for all earthquakes from 2010 to 2022 with MW ≥ 7.5 and depth less than 200 km (56 events). The method provides automatic estimates of rupture length, directivity, speed, and aspect ratio, a proxy for rupture complexity. We obtained short‐period rupture length scaling relations that are in good agreement with previously published relations based on estimates of total slip. Rupture speeds were consistently in the sub‐Rayleigh regime for thrust and normal earthquakes, whereas a tenth of strike‐slip events propagated at supershear speeds. Many rupture histories exhibited complex behaviors, for example, rupture on conjugate faults, bilateral propagation, and dynamic triggering by a P wave. For megathrust earthquakes, ruptures encircling asperities were frequently observed, with downdip, updip, and balanced patterns. Although there is a preference for short‐period emissions to emanate from central and downdip parts of the megathrust, emissions updip of the main asperity are more frequent than suggested by earlier results.
... For all the stations, we used records of teleseismic earthquakes with magnitude ≥5.5 and epicentral distances between 30°and 90°. The seismograms were time-windowed between 20 s before and 50 s after the theoretical P-wave arrival time, calculated using the IASP91 reference model (Kennett & Engdahl, 1991). We calculated two suites of RFs from the data as described in Section 2.3 above. ...
... For station G22A, Vp of 3.6 and 6.7 km/s were used for the sediment and sub-sediment layer, respectively (Yeck et al., 2013). For the upper mantle properties, we used the IASP91 model (Kennett & Engdahl, 1991). In the waveform-fitting step of our new approach, we allowed for ±1 km (with 0.1 km step) freedom to the thickness of the sediment derived from the H-κ stacking to account for the uncertainties in the estimation of the Vp of the sediment layer (Section 3). ...
The receiver function technique is widely used to image crustal structure using P‐to‐S converted phases at the Moho discontinuity. However, the presence of sedimentary layer generates additional P‐to‐S conversions and reverberations, which can overprint the Moho phases and pose problems in imaging crustal structure with standard receiver function techniques. We introduce a robust two‐step method that uses H‐κ stacking to determine average thickness and Vp/Vs of the sedimentary layer, followed by waveform‐fitting of the observed receiver function to constrain the average crustal thickness and sub‐sediment Vp/Vs. We tested the method using both synthetic data and real‐data from stations located on sedimentary layers in the Netherlands and USA. We show that the new method outperforms other common approaches in retrieving accurate Moho depth and sub‐sediment Vp/Vs estimates, even in cases where the Moho phases are completely overprinted by large‐amplitude phases related to sedimentary layers.
... Three-dimensional wave propagation effects that cannot be described by the assumed AK-135 1-D layered Earth structure model (Kennett and Engdahl, 1991) cause shifts in the wave arrival time and these in turn bias the semblance map. To mitigate this effect and to reduce the absolute location error of the multi-array semblance map we estimate empirical travel time shifts and calibrate the waveform data before stacking at each station (Palo et al., 2014;Ishii et al., 2007;Meng et al., 2016;Fan and Shearer, 2017). ...
... We used the same station setup and data processing as for the real data BP. Synthetic waveforms were calculated at a sample rate of 4 Hz using a Green's function store calculated with QSEIS and the AK-135 Earth structure model (Kennett and Engdahl, 1991). For both synthetic BPs we observe early bilateral rupture due to the abrupt stopping of the rupture at the model-fault edges. ...
The Gulf of Aqaba earthquake occurred on 22 November 1995 in the Northern Red Sea and is the largest instrumentally recorded earthquake in the region to date. The event was extensively studied during the initial years following its occurrence. However, it remained unclear which of the many faults in the gulf were activated during the earthquake. We present results from multi-array back projection that we use to inform Bayesian kinematic rupture models constrained by geodetic and teleseismic data. Our results indicate that most of the moment release was on the Aragonese fault via left-lateral strike slip and shallow normal faulting that may have been dynamically triggered by an early rupture phase on the Arnona fault. We also identified a predominantly normal fault-segment on the eastern shore of the gulf that was activated in the event. We dismiss the previously proposed hypothesis of a co-seismic sub-event on the western shore of the gulf and confirm that observed deformation can be rather attributed to post-seismic activity. In conclusion, the gulf shows many signs of active tectonic extension. Therefore, more events close to the shorelines are to be expected in the future and should be considered conducting infrastructure projects in the region.
... The traces were then rotated from the geographic coordinate system (Z-N-E) to the local P-SV-SH ray-based coordinate system (Vinnik, 1977;Kind et al., 1995;Dahl-Jensen et al., 2003). Theoretical arrival times were then calculated by using the IASP91 model (Kennett and Engdahl, 1991), and relative travel-time residuals were then measured. The waveforms were aligned along the S-phase arrival for each event using a multichannel cross-correlation algorithm (VanDecar and Crossen, 1990). ...
... After deconvolution, the data were reinspected, and anomalous traces were deleted. To suppress noise and enhance spatial consistency of Sp conversion phase from the LAB, we first continuously performed a move-out correction of raw SRFs in the time-domain with a constant ray parameter of 0.0573 s/km (corresponding to slowness of 6.4 s/ • or an epicentral distance of 67 • ) by using the iasp91 1D velocity model (Kennett and Engdahl, 1991), and then conducted common conversion point (CCP) stacking (Dueker and Sheehan, 1997;Kosarev et al., 1999;Zhu, 2000Zhu, ,2002 and migrated it into the depth domain referring to the IASP91 model. appeared around ~55-65 km depth in the CCP stacked sections of the SRFs which we interpret as LAB. ...
Detailed knowledge of the lithospheric thickness is important for understanding the tectonic evolution in central Eastern China, characterized by ore deposits in the Middle-Lower Yangtze Metallogenic Belt (MLYMB). We realize this goal by applying the common conversion point (CCP) stacking to Sp receiver functions (SRF) computed from 234 broadband seismic stations in central Eastern China. Distinct negative signals are identified below the Moho in all the CCP stacking profiles, which we interpret as the S-to-P conversions from the lithosphere-asthenosphere boundary (LAB). The imaged LAB is as shallow as ∼60 km with a standard deviation of ∼5 km in the whole region, in contrast to the typical cratonic lithosphere root down to 200 km depth or more, indicating the widespread lithospheric thinning in the study region. Such a flat LAB indicates that the regional lithosphere has been destructed uniformly, shedding light on its destructive mechanism, which we attribute to lithospheric delamination along a mid-lithospheric discontinuity (MLD). Compared to the MLD (∼80–100 km) observed in the western North China Craton, our observations suggest that the destructed lithosphere probably has been further stretched due to slab rollback and trench retreat. In contrast, lithospheric cooling-induced accretion plays a minor role in the lithospheric evolution after destruction.
... The SURF96 (Hermann 1987(Hermann , 2004 software has been used for the inversion of Bnal average Rayleigh waves dispersion curves (at 7-87 s) and Love waves (at 7-82 s) (Bgures 4a, b) to compute the Bnal average one-dimensional regional V s structure below North India. The initial 1-D velocity for the crustal region has been obtained from Dube et al. (1973), and the starting velocity model for the upper-mantle part (from crust-mantle boundary to 140 km) constrained by the subcrustal V s structure of the IASP91 (Kennett and Engdahl 1991). First, our starting velocity model was a 38.7-km thick two-layered crustal model. ...
... We take into consideration an additional initial velocity model in which the subcrustal component is constrained by the V s structure of the IASP91 (Kennett and Engdahl 1991) model and the crustal component is constrained by the V s model developed by Dube et al. (1973) (Bgure 5c). Taking into account the value of V p /V s = 1.732, the Moho is at a depth of 38.7 km. ...
... The details of CCP imaging methodology have been discussed in Caldwell et al. (2013) and the manual of Funclab (Eagar, 2012). Here, we used the 1-D IASP91 velocity model for the CCP imaging (Kennett & Engdahl, 1991). We have performed CCP imaging along three profiles (EW striking AB, NS striking CD, and NW-SE trending EF), whose locations are shown in Fig. 1a. ...
... It is noteworthy to observe that the time difference between the 410-km and 660-km conversions is consistently 24 s at the majority of the stations (see Figs. 4, 5, 6; Table 1). This value aligns with the theoretical time difference predicted by the IASP91 velocity model (Kennett & Engdahl, 1991) for these two phases. The aforementioned observation indicates that there is no significant variation in the boundaries at 410-and 660-km depths below the specified region. ...
To monitor seismicity, a 10-station broadband seismic network was deployed in the Hyderabad region by CSIR-NGRI, Hyderabad, India, during 2020–2021. The analysis of radial P- receiver functions (PRFs) using data from this network detects conversions from five major crustal and mantle discontinuities below the region. Our CCP stacking of radial PRFs also images the nature and geometry of these seismic discontinuities viz., Moho (increase in positive amplitude at 30–40 km depths), Hales discontinuity (increase in positive amplitude at 90–120 km depths), lithosphere-asthenosphere boundary (LAB) (increase in negative amplitude at 130–160 km depths), 410-km (increase in positive PRF amplitude at 410–440 km depths) and 660-km (increase in positive PRF amplitude at 620–660 km depths). Our modeling also reveals that the mean depth to the Moho, Hales discontinuity (H-D) and LAB below the study region are 36, 115 and 160 km, respectively, suggesting the absence of a thick cratonic root below the EDC. We interpret the H-D boundary (at 90–125 km depths) below the Hyderabad region as a lithologic boundary between upper mantle peridotite and eclogite resulted from the Archean subduction. We also model the differential time of the 410- and 660-km conversions, which is found to be 24 s at most of the stations that is the same as the theoretical differential time between these two phases according to the IASP91 global reference velocity model, indicating a typical cratonic behaviour of the EDC. However, a noticeable upward movement of the 410-km discontinuity and a slight downward movement of the 660-km discontinuity below the central part of the study region is also modelled that suggests a thickening of the Mantle transition zone, which could be attributed to the presence of probable imprints of the Archean subduction below the Hyderabad, EDC, India.
... We run SUGAR with this data set and ask a professional seismic analyst who has extensive experience with Kaikoūra aftershocks to work on it for comparison. SUGAR and the analyst use the same "iasp91" 1D velocity model (Kennett & Engdahl, 1991). The analyst has the prior knowledge that the data set is synthetic for the Kaikora region and the waveforms were generated with a different velocity model. ...
Seismic source locations are fundamental to many fields of Earth and planetary sciences, such as seismology, volcanology and tectonics. However, seismic source detection and location are challenging when events cluster closely in space and time with signals tangling together at observing stations, such as they often do in major aftershock sequences. Though emerging algorithms and artificial intelligence (AI) models have made processing high volumes of seismic data easier, their performance is still limited, especially for complex aftershock sequences. In this study, we propose a novel approach that utilizes three‐dimensional image segmentation—a computer vision technique—to detect and locate seismic sources, and develop this into a complete workflow, Source Untangler Guided by Artificial intelligence image Recognition (SUGAR). In our synthetic and real data tests, SUGAR can handle complex, energetic earthquake sequences in near real time better than skillful analysts and other AI and non‐AI based algorithms. We apply SUGAR to the 2016 Kaikōura, New Zealand sequence and obtain five times more events than the analyst‐based GeoNet catalog. The improved aftershock distribution illuminates a continuous fault system with extensive fracture zones beneath the segmented, discontinuous surface ruptures. Our method has broader applicability to non‐earthquake sources and other time series image data sets.
... Using V2RhoT_gibbs 48,51 , the algorithm determines the stable state in terms of phase and mineral assemblages based on an augmented and modified version 57 of an original thermodynamic database 58 . Thereby, pressure is approximated as lithostatic load using the density information of a reference model 53 seismically equivalent to the standard seismological ak135 model 59 . ...
The distribution of earthquakes in stable intracontinental tectonic settings is typically far more diffuse than along plate boundaries and the causative mechanisms underlying some recognizable clustering are not understood. Here we show that seismicity in intraplate western and central Europe is largely limited to regions that exhibit a low-density layer in the uppermost lithospheric mantle and preferentially clustered above lateral gradients in upper mantle effective viscosity. The basis for these new insights into the thermal and density configuration of the upper mantle is provided by a shear-wave tomographic model. We propose that the spatial correlations between mantle low-density bodies and crustal seismicity reflect the importance of buoyancy forces within the mantle lithosphere. In addition, under the interaction of forces due to mantle gravitational instabilities, plate tectonics and postglacial rebound, the variably hot and strong mantle lithosphere responds by localized deformation which imposes differential loading on the overlying crust.
... The lithosphere structure beneath these stations can be roughly divided into two types (Figures 4b and 4c). The type 1 model is quite similar to the standard iasp91 model (Kennett & Engdahl, 1991), and the type 2 model has a relatively shallow Moho. We use these two models combined with the PREM attenuation model (Dziewonski & Anderson, 1981) to compute the 1-D DSM wavefield. ...
Accurate source parameters of global submarine earthquakes are essential for understanding earthquake mechanics and tectonic dynamics. Previous studies have demonstrated that teleseismic P coda waveform complexities due to near‐source 3‐D structures are highly sensitive to source parameters of marine earthquakes. Leveraging these sensitivities, we can improve the accuracy of source parameter inversion compared to traditional 1‐D methods. However, modeling these intricate 3‐D effects poses significant computational challenges. To address this issue, we propose a novel reciprocity‐based hybrid method for computing 3‐D teleseismic Green's functions. Based on this method, we develop a grid‐search inversion workflow for determining reliable source parameters of moderate‐sized submarine earthquakes. The method is tested and proven on five Mw5+ earthquakes at the Blanco oceanic transform fault (OTF) with ground truth locations resolved by a local ocean bottom seismometer array, using ambient noise correlation and surface‐wave relocation techniques. Our results show that fitting P coda waveforms through 3‐D Green's functions can effectively improve the source location accuracy, especially for the centroid depth. Our improved centroid depths indicate that all the five Mw5+ earthquakes on the Blanco transform fault ruptured mainly above the depth of 600°C isotherm predicted by the half‐space cooling model. This finding aligns with the hypothesis that the rupture zone of large earthquakes at OTFs is confined by the 600°C isotherm. However, it is noted that the Blanco transform fault serves as a case study. Our 3‐D source inversion method offers a promising tool for systematically investigating global oceanic earthquakes using teleseismic waves.
... Before utilizing Eq. 1, we follow the procedures for preprocessing the RFs to improve the accuracy of the measurements. Firstly, to minimize the moveout caused by epicentral distances, all RFs were adjusted to a consistent ray parameter of 0.06 s/km utilizing the IASP91 model (Kennett and Engdahl, 1991). Secondly, considering this dense array with limited useful RFs in a single station, we stored the RFs of the 21 nearby stations for the center stations. ...
The Ailaoshan Orogenic Belt (AOB), located at the southeastern boundary of the Tibetan Plateau, is an ideal place for investigating the mechanisms of lateral growth of Tibet. Using the data recorded by a dense seismic array across the Ailaoshan belt, we investigate the detailed lateral variations of crustal anisotropy on the basis of Pms phase of receiver functions. Remarkable crustal anisotropy is observed throughout this study region with a mean delay time of 0.33 ± 0.19 s, indicating the anisotropy primarily originates in the middle-lower crust. The fast directions beneath the AOB including the Ailaoshan-Red River shear zone (ARRSZ) and its western low-grade metamorphic unit generally align with the NW-SE strike of ARRSZ. The weak anisotropy in the South China Block (SCB) argues that the block is relatively stable, with limited internal deformation. Meanwhile, the anisotropy beneath the western boundary of the SCB is strong, and the N-S oriented fast direction is influenced by both the crustal stress and Xiaojiang Fault. Combining the high Vp/Vs and significant lateral variations of crustal anisotropy parameters, we suggest that the strike-slip motion along the ARRSZ induces the partial melting and pronounced anisotropy in the middle-lower crust of AOB, without the presence of crustal flow. The differences between crustal and mantle anisotropy indicate crust-mantle decoupling deformation of the AOB, supporting the block extrusion model occurring only in the crustal scale as the primary deformation pattern.
... To eliminate the influence of varying epicentral distances on the arrival time variations of Pms, the RFs need to be corrected for a consistent equivalent hypocentral distance and the same source depth. In this study, according to the IASP91 model (Kennett & Engdahl, 1991), the arrival times of Pms relative to the direct P wave were uniformly corrected to an epicentre distance of 60° with a depth of 0 km. As the Pms arrival time varies with BAZ in the cosine function, the nonlinear least squares method is used to fit the Pms arrival time to Equation (1) to obtain the crustal anisotropy parameters ( Figure 3). ...
The mechanisms of uplift and deformation of the Tibetan Plateau are highly concerned. Understanding the crustal deformation mechanisms beneath southeast Tibet is important as it is located at the major path of Tibet's growth or expansion. Recent studies are controversial on whether large‐scale crustal flow is dominant or not in this area. We applied Pms arrival time technique based on receiver function to events from 10 years of observation and obtained the crustal anisotropy parameters. The results show that both the large‐scale faults and local crustal flow play major roles in crustal deformation in interested areas, while the large‐scale crustal flow is not very well preferred. Furthermore, the crustal anisotropy in southeast of the study area is characterized by complex anisotropies, which may be potentially related to the converging of two mantle flows from various origins.
... The third part includes P-wave arrival-time data of local and regional earthquakes recorded at ocean bottom seismometers in the Yap subduction zone 47 (purple triangles in Fig. 1), which were deployed and retrieved by the Institute of Oceanology, Chinese Academy of Sciences, using the research Vessel KEXUE. The P-wave arrival times of local and regional events recorded at the ocean bottom seismometers are manually picked based on theoretical arrival times computed for the IASP91 Earth model 48 and merged with the ISC-EHB data. ...
Seismic anisotropy could provide vital information about the evolution and internal convection of the deep Earth interior. Although previous seismological studies have revealed a wide distribution of seismic anisotropy in the upper portion of the lower mantle beneath many subduction zones, the existence of anisotropy at these depths away from subducted slabs remains debated. Here we use P-wave azimuthal anisotropy tomography to image the crust and mantle down to 1,600-km depth. We find prominent anisotropic patterns in the upper portion of the lower mantle beneath the Philippine Sea Plate. Substantial azimuthal anisotropy with N–S fast-velocity directions occurs at 700–900-km depths. We interpret this azimuthal anisotropy as a remnant of the Pacific lower mantle flow field about 50 million years ago. Two isolated high-velocity anomalies at 700–1,600-km depths may be vestigial pieces of the subducted Izanagi slab with seismic velocity features suggesting a shift in the Pacific lower mantle flow field by about 40 million years ago. Our findings provide seismic evidence for the existence of complex lower mantle flows and deformation mechanisms away from subduction zones.
... We constructed a detailed crustal structure along the linear seismic array by using the CCP technique 60 . We obtained the ray-paths of the receiver function by using the IASP91 velocity model 58 . Each amplitude on the receiver function following the direct P-wave was assumed to be generated by the Ps conversion on a seismic discontinuity along the theoretical ray path. ...
The Dunhua-Mishan fault, located in the northern segment of the Tanlu fault zone, experienced multiple tectonic processes associated with the effects of the Pacific Plate subduction and the Indo-Asia collision. The high-resolution fault-scale structure is critical for understanding the fault evolution and potential fault damage. However, the well-defined deep structure of the Dunhua-Mishan fault is still unclear due to the lack of the dense seismic array. In this study, we construct a high-resolution P-wave receiver function imaging based on linear dense seismic array across the fault. Our results reveal the strong Moho depth variation across the Dunhua-Mishan fault zone. The slightly higher Vp/Vs ratio values within the fault zone indicate the presence of a small amount of mafic crust composition. Interestingly, the significant double positive Ps converted phases are observed within the fault zone, which may represent double Moho discontinuities. The double Moho structure may be related to multiple significant tectonic activities in the Tanlu northern segment. These newly observed structures provide new seismic constraints on the formation and evolution of the Tanlu fault zone and probably reflect that the lithospheric structure of the Dunhua-Mishan fault has been modified by a series of tectonic processes.
... We find four non-ISC events (referred to as events not documented by the ISC catalog) that generate clear Pwaves and S-waves at nearby onshore stations ( Figure S1 in Supporting Information S1). To determine their origin times and locations, we perform a grid search with an interval of 0.02°, minimizing the L1 norm of the time differences between predicted and manually picked P and S arrivals (see Text S1 in Supporting Information S1 for more details; Kennett & Engdahl, 1991). All of them are located in regions of active background seismicity close to the continental shelf-two near the Explorer Ridge and the other two to the north of the NEPTUNE array ( Figure 2a and Figure S1 in Supporting Information S1). ...
A T‐wave is a seismo‐acoustic wave that can travel a long distance in the ocean with little attenuation, making it valuable for monitoring remote tectonic activity and changes in ocean temperature using seismic ocean thermometry (SOT). However, current high‐quality T‐wave stations are sparsely distributed, limiting the detectability of oceanic seismicity and the spatial resolution of global SOT. The use of ocean bottom distributed acoustic sensing (OBDAS), through the conversion of telecommunication cables into dense seismic arrays, is a cost‐effective and scalable means to complement existing seismic stations. Here, we systematically investigate the performance of OBDAS for oceanic seismicity detection and SOT using a 4‐day Ocean Observatories Initiative community experiment offshore Oregon. We first present T‐wave observations from distant and regional earthquakes and develop a curvelet denoising scheme to enhance T‐wave signals on OBDAS. After denoising, we show that OBDAS can detect and locate more and smaller T‐wave events than regional OBS network. During the 4‐day experiment, we detect 92 oceanic earthquakes, most of which are missing from existing catalogs. Leveraging the sensor density and cable directionality, we demonstrate the feasibility of source azimuth estimation for regional Blanco earthquakes. We also evaluate the SOT performance of OBDAS using pseudo‐repeating earthquake T‐waves. Our results show that OBDAS can utilize repeating earthquakes as small as M3.5 for SOT, outperforming ocean bottom seismometers. However, ocean ambient natural and instrumental noise strongly affects the performance of OBDAS for oceanic seismicity detection and SOT, requiring further investigation.
... In the initial 1-D velocity model (Fig. S5), Vp is 6.1, 6.4 and 6.8 km/s in the upper, middle and lower crust, respectively, and we adopt the iasp91 model (Kennett and Engdahl, 1991) for the mantle velocity. We apply the LSQR technique (Paige and Saunders, 1982) with smoothing and damping regularizations to solve the system of observation equations relating the travel-time data with the unknown parameters, i.e., the hypocentral parameters of local events and the dVp values at 3-D grid nodes (for details, see Zhao et al., 1994Zhao et al., , 2012. ...
Earthquakes deeper than 60 km generally occur in subducting slabs. However, on 21 September 2013 two earthquakes (M4.8 and M3.0) occurred at ~71-75 km depths in the upper mantle beneath central Wyoming in the stable North American continent, where there is no actively subducting slab at present. The cause of the two events is still unclear. Here we present detailed 3-D P-wave isotropic and anisotropic tomography down to 750 km depth under Wyoming and adjacent areas. Our result shows that the two Wyoming events took place within a high-velocity (high-V) body at 0-160 km depths, which may be part of dense continental lithosphere. Another high-V body exists at ~300-500 km depths, which may reflect a remnant of the subducted Farallon slab. A significant low-velocity (low-V) zone appears at ~200-300 km depths between the two high-V bodies, and the low-V zone exhibits seismic anisotropy that Vp is greater in the vertical direction than that in the horizontal direction. The low-V zone may include ascending fluids from dehydration of the subducted slab remnant, which was promoted by the nearby hot Yellowstone plume. It is highly possible that the ascending fluids induced the 2013 Wyoming upper-mantle earthquakes.
... For computational efficiency, we assume 1D rays predicted via the TauP toolkit (e.g., Crotwell et al., 1999). The reference model is IASP91 (e.g., Kennett and Engdahl, 1991), which closely resembles the far-field velocity profile through the geodynamic model. Although still applicable, we observe that the ray-based approach outlined here is not well suited for the inversion of core-converted phases alone due to their near-vertical incidence angles, and hence poor depth resolution when finite-frequency effects are not taken into consideration (e.g., Chevrot, 2006;Mondal and Long, 2019). ...
Underdetermination is a condition affecting all problems in seismic imaging. It manifests mainly in the nonuniqueness of the models inferred from the data. This condition is exacerbated if simplifying hypotheses like isotropy are discarded in favor of more realistic anisotropic models that, although supported by seismological evidence, require more free parameters. Investigating the connections between underdetermination and anisotropy requires the implementation of solvers which explore the whole family of possibilities behind nonuniqueness and allow for more informed conclusions about the interpretation of the seismic models. Because these aspects cannot be investigated using traditional iterative linearized inversion schemes with regularization constraints that collapse the infinite possible models into a unique solution, we explore the application of transdimensional Bayesian Monte Carlo sampling to address the consequences of underdetermination in anisotropic seismic imaging. We show how teleseismic waves of P and S phases can constrain upper-mantle anisotropy and the amount of additional information these data provide in terms of uncertainty and trade-offs among multiple fields.
... The tomographic method is able to deal with complex-shaped velocity discontinuities in the study volume such as the Moho and the subducting slab boundary. Previous studies have shown that the subducted slab in a subduction zone often cannot be well resolved by a tomographic inversion with a pure 1-D starting model such as the IASP91 Earth model (Kennett and Engdahl, 1991), because the distributions of seismic stations, local and teleseismic events are nonuniform and the crisscross of ray paths is imperfect (e.g., Zhao et al., 1992;Liu et al., 2014;Wang and Zhao, 2021;Jia and Zhao, 2023). To better constrain the 3-D velocity structure, we adopt a starting model that includes the pre-set MS slab whose upper surface is extracted from the Slab2 model and has been well constrained by the local seismicity (Hayes et al., 2018). ...
The Molucca Sea region is an active arc-arc collision zone whose structure and mantle dynamics are essential for reconstructing the tectonic evolution of Southeast Asia. The key to understanding the tectonic processes of the region is to clarify the morphology of the subducted slabs. However, geometric details of the subducted Molucca Sea slab and other slab segments under this region remain controversial due to the lack of high-resolution mantle tomography. In this study, we jointly invert a large number of local and teleseismic travel-time data recorded at 99 local seismic stations to determine a high-resolution model of P-wave tomography beneath the Molucca Sea region. Our tomography reveals two aseismic slab segments in the deep upper mantle and the mantle transition zone, which may reflect the earlier subducted Molucca Sea slab. The total length of the Molucca Sea slab is estimated to be ~1800 to 1900 km, being ~300 km longer than previous estimates.
... The numbers of P-and S-phase picks at each station are shown in Table S1. We first used the IASP91 velocity model by Kennett and Engdahl (1991) as a P-and S-initial model and perturbed the velocity of every layer by as much as ± 5-15% to gain 100 new initial models (see Fig. S1). The final model was estimated by taking the average of 5 velocity models with the lowest RMS residuals, which yielded a final P-velocity model with RMS residual at ~ 0.4 s. ...
Two moderate earthquakes struck the South-Central part of Java Island (in Indonesia’s archipelago) with Mw 5.7 and Mw 5.9 on June 06 and June 30, 2023, respectively. Both earthquakes were followed by ~100 aftershocks with widespread and strong impacts along Java Island where some regions suffered several damages. In this study, both earthquake mechanisms were derived from the Bayesian moment tensor inversion and configure a unique faulting with a thrusting mechanism that is striking perpendicularly with the trench in the N–S direction. The results of the hypocenter relocation, using an updated 1-D velocity model, show that the aftershocks of the Mw 5.9 occurred deeper than the interface zone, while the aftershocks of the Mw 5.7 were located shallower above the slab. Both earthquakes can robustly confirm possible evidence of different faulting vertically clustered above the intraslab zone. The Mw 5.9 can be assumed as the backstop system dipping to the east–west direction, while Mw 5.7 is the backthrust system with south-dipping. Furthermore, a broad impact of both earthquakes on the resilience of MMI VI intensity with PGA value > 100 gal can be used to update the mitigation plan for the intraslab earthquake in the near future.
... A linear interpolation of the cumulative elastic response evaluated at the monthly intervals is subtracted from U obs . For this, we convolve mass loss of the GrIS and PGs with the vertical displacement Green's functions derived by Wang et al. (2012) for the elastic Earth model iasp91 (Kennett & Engdahl, 1991) with refined crustal structure from Crust 2.0 (Bassin et al., 2000). ...
Greenland's bedrock responds to ongoing ice loss with an elastic vertical land motion (VLM) that is measured by Greenland's Global Navigation Satellite System (GNSS) Network (GNET). The measured VLM also contains other contributions, including the long‐term viscoelastic response of the Earth to the deglaciation of the last glacial period. Greenland's ice sheet (GrIS) produces the most significant contribution to the total VLM. The contribution of peripheral glaciers (PGs) from both Greenland (GrPGs) and Arctic Canada (CanPGs) has not carefully been accounted for in previous GNSS analyses. This is a significant concern, since GNET stations are often closer to PGs than to the ice sheet. We find that, PGs produce significant elastic rebound, especially in North and East Greenland. Across these regions, the PGs produce up to 32% of the elastic rebound. For a few stations in the North, the VLM from PGs is larger than that due to the GrIS.
... The first step of optimisation is to define an initial model space. We initiate a model with two major discontinuities at the depths proposed by the global standard model IASP91 (Kennett & Engdahl, 1991) and use an approximate S-wave velocity model according to the observed V S,app curve. This approximation ensures that the difference between the initial and the true S-wave velocity is small enough so that the assumption of linearisation in the process of calculating RF R and V S,app Jacobians is valid. ...
Receiver function (RF) inversion is a well-established method to quantify a horizontally layered approximation of the S-wave velocity structure beneath a seismic station. It is well-known that the RF inverse problem is highly non-unique, and various tools such as joint inversion with other seismological observations exist that may overcome this problem. We present a joint inversion framework along with a Python package that implements the joint inversion of RF and the apparent S-wave velocity (VS,app). Our implementation includes a pseudo-initial model estimation, which helps address the inherent non-uniqueness of the joint inversion of RFs and VS,app. This implementation enhances the resolving power, enabling estimation of S-wave velocities with resolution approaching that of deep controlled source seismic methods. As an illustration, we showcase an example from a permanent station in the Makran subduction zone southeast of the Iranian Plateau and two other stations in the supplementary material. We compare our joint inversion results with several S-wave velocity models obtained through a deep seismic sounding profile and joint inversion of surface wave dispersion and RFs. This comparison shows that although we note a slightly lower sensitivity of our proposed method at greater depths (beyond 50 km), the method yields much better results for shallow structures. Our inversion code provides a powerful, accessible software package that has superior resolving power at shallow depth compared to RFs-surface wave inversion codes. Furthermore, the fact that only one data-derivative is used, makes this inversion code extremely easy to use, without the need for complementary datasets.
... As the data processing for receiver function imaging is fairly standardized, here we only briefly introduce the processing workflow and focus more on the validation procedures. We first correct the instrument response and cut seismograms associated with each earthquake using a window of 10 s before and 50 s after the predicted P wave arrivals using the IASP91 model (Kennett & Engdahl, 1991). We then rotate the three-component earthquake recordings to the radial-vertical components for each earthquake and station pair. ...
Plain Language Summary
Mapping the detailed crustal structure plays a critical role in ore characterization and exploration, which is essential to keep pace with societal needs for green energy and sustainability. Here we apply seismic imaging to delineate the subsurface structure of the Nanling metallogenic belt in South China using hundreds of sensors. We find the crustal structure, particularly the Moho geometries, spatially correlates with the types of ore deposits. Specifically, the tin and tungsten‐tin‐bearing granites that have mantle chemical signatures are distributed near a major fault zone with a gradual crust‐mantle transition. In contrast, tungsten and other metal deposits in the central belt show evidence of mostly crustal origin with a seismically sharp and elevated Moho. We propose that the imaged gradual crust‐mantle transition, which corresponds likely to an inherited lithospheric weak zone, could serve as a magmatic pathway for mantle materials to flux into the lower crust, thus contributing to critical ore deposits.
... However, there is not much improvement on the depth of the earthquake because most of them have a depth of 10 km (fixed depth). The fixed depth often happens because hypocenter determination using SeisComp4 still uses the global velocity model IASP91 [7]. ...
The BMKG earthquake catalog data for the 2014-2022 period shows seismic activity in the Gumai Mountains, South Sumatra, which is located southeast of the Ketaun Segment, east of the Musi Segment, and north of the Manna Segment. Seismic activity in this area is important to study as an early indication of the presence of other active fault segments that have not been identified before. Re-analysis on the P and S wave phases picking was carried out for the 26 earthquakes in the period of 2014 to 2022 to ensure the quality of the data used in the processing. The double-difference method was then used to relocate the hypocenter of the earthquake based on a local velocity model to identify an active fault segment lineation in the area. In addition, waveform inversion method was used to obtain the focal mechanism for 7 earthquakes which were successfully analyzed to identify the fault plane direction. By combining the results of seismicity and focal mechanism analysis, we concluded that there are 3 fault segments that have not been identified before. These segments are thought to be strongly responsible for seismic activity in Gumai Mountains in Lahat and Empat Lawang Regencies, South Sumatra, which we determine to be part of the Great Sumatran Fault network.
... Then, the MCCC technique is employed to accurately measure the differential traveltimes of first P-arrivals (VanDecar & Crosson, 1990). To avoid subjective selection of cross-correlation time window, we test 11 time windows, beginning at 5 s before the theoretical arrival time computed in the AK135 model (Kennett & Engdahl, 1991) and having varying lengths ranging from 15 to 25 s with a gap of 1 s. The differential traveltime is chosen based on the highest cross-correlation coefficient among all time windows (see an example in Figure 3). ...
We propose a novel framework for teleseismic traveltime tomography that requires no ray tracing. The tomographic inverse problem is formulated as an Eikonal equation‐constrained optimization problem, aiming at the determination of a slowness model that minimizes the difference between observational and predicted differential traveltimes. Two improvements have been made over previous ray‐based methods. First, the traveltimes from the source outside the study region to any positions within the study region are computed using a hybrid approach. This involves solving a 2D Eikonal equation to obtain the traveltimes from the source to the boundary of the study region and solving a 3D Eikonal equation to compute the traveltimes from the boundary to any positions within the study region. Second, we compute the sensitivity kernel using the adjoint‐state method. This method avoids the computation of ray paths and makes the computational cost nearly independent of the number of receivers. We apply our new method in Thailand and adjacent regions. The final velocity model reveals a thick lithosphere beneath the Khorat Plateau and two mantle upwelling branches beneath its southern and western margins. The mantle upwelling may result from the mantle convection triggered by surrounding subduction systems and/or a slab window of the Indian Plate. The presence of the mantle upwelling corresponds to the source zone of the erupted Cenozoic basalts in the Khorat Plateau, indicating lithospheric modification beneath the plateau. The insightful tomographic result verifies our method and provides new perspectives on the structural heterogeneities and dynamics of the Indochina Block.
This paper presents an integrated seismic study of the Eastern Iranian Ranges (EIR), examining the lithospheric and mantle dynamics since the region's formation in the Late Cretaceous. Through analysis of receiver function (RF) waveforms and inversion with Rayleigh wave velocity data, we unveil west-dipping lithospheric structures and a distinctive deepening of the Moho under the EIR, connoting complex intra-continental tectonics. Moreover, interpreting teleseismic records using non-linear tomography highlights stark mantle velocity contrasts, suggesting lithospheric dripping and consequential asthenospheric rise that may drive the EIR's post-collisional magmatism and topographic anomalies. Our findings portray the underthrusting of the Eurasian margin and possible lithospheric delamination as significant contributors to the EIR's orogenic development, reflecting an intricate coupling of deep geodynamic mechanisms with surface geological features.
The mechanisms governing a commonly observed seismic velocity drop in the cratonic lithosphere, referred to as the mid‐lithospheric discontinuity (MLD), have been widely debated. To identify the composition and seismic structure of MLDs, we have analyzed Sp receiver functions (SRF) and mantle xenocrysts for six regions across Australia. We utilize locations where seismic stations and kimberlite‐hosted mantle xenocrysts are both available, allowing for comparison between seismological and petrological constraints. Our results show negative SRF phases indicative of the MLD coincide with clinopyroxene‐depleted zones at 60–140 km depth. Clinopyroxenes with different chemical compositions across the MLD define a litho‐chemical discontinuity. Modeling and experimental data show that MLDs may be explained by modified lherzolite with 10%–20% modal pargasite. Pargasite MLDs may form when rising H2O‐bearing melts cross the amphibole dehydration curve and react with clinopyroxene in lherzolite. Because the amphibole dehydration curve is isobaric at 80–120 km, pargasite will be precipitated as horizontal channels.
We proposed a deep learning (DL) method to derive VS models from joint inversion of Rayleigh-wave dispersions and receiver functions, which is based on multilabel convolutional neural network and recurrent neural network. We used a spline-based approach to generate synthetic models instead of directly using existing models to build the training data set, which improves the generalization of the method. Unlike the traditional methods, which usually set a fixed VP/VS ratio, our method makes full use of the powerful data mining ability of DL to invert the VS models assuming different VP/VS ratios. A loss function is specially designed that focuses on key features of the model space, for example, the shape and depth of Moho. Synthetic tests demonstrate that the proposed method is accurate and fast. Application to the southeast margin of the Tibetan Plateau shows results consistent with the previous joint inversion with P constraints, indicating the proposed method is reliable and robust.
The unprecedentedly dense current sampling of the upper mantle with seismic data offers an opportunity for determining representative seismic velocity models for the Earth’s main tectonic environments. Here, we use over 1.17 million Rayleigh- and 300,000 Love-wave, fundamental-mode, phase-velocity curves measured with multimode waveform inversion of data available since the 1990s, and compute phase-velocity maps in a 17–310 s period range. We then compute phase-velocity curves averaged over the globe and eight tectonic environments, and invert them for 1D seismic velocity profiles of the upper mantle. The averaged curves are smooth and fit by VS models with very small misfits, under 0.1%, at most periods. For phase-velocity curves extending up to 310 s, Rayleigh waves resolve VSV structure down to the shallow lower mantle. Love-wave sampling is shallower, and VSH and, thus, radial anisotropy profiles are resolved down to 375–400 km depth. The uncertainty of the VS models is dominated by the trade-offs of VS at neighboring depths. Using the model-space-projection approach, we quantify the uncertainty of VS in layers of different thickness and at different depths, and show how it decreases with the increasing thickness of the layers. Example 1D VS models that fit the data display the expected increase of the lithospheric seismic velocity with the age of the oceanic lithosphere and with the average age of the continental tectonic type. Radial anisotropy in the global and most tectonic-type models show a flip of the sign from positive (VSH>VSV) to negative at 200–300 km depth. Negative anisotropy is also observed in the shallow mantle lithosphere beneath oceans down to 45–55 km depth. We also compute a global model with the minimal structural complexity, which fits the data worse than the best-fitting one but does not include a sublithospheric low-velocity zone, providing a simple reference for seismic studies.
Seismic travel time anomalies of waves that traverse the uppermost 100-200 km of the outer core have been interpreted as evidence of reduced seismic velocities (relative to radial reference models) just below the core-mantle boundary. These studies typically investigate differential travel times of SmKS waves, which propagate as P-waves through the shallowest outer core and reflect from the underside of the core-mantle boundary m times. The use of SmKS and S(m-1)KS differential travel times for core imaging are often assumed to suppress contributions from earthquake location errors and unknown and unmodelled seismic velocity heterogeneity in the mantle. The goal of this study is to understand the extent to which differential SmKS travel times are, in fact, affected by anomalous mantle structure, potentially including both velocity heterogeneity and anisotropy. Velocity variations affect not only a wave's travel time, but also the path of a wave, which can be observed in deviations of the wave's incoming direction. Since radial velocity variations in the outer core will only minimally affect the wave path, in contrast to other potential effects, measuring the incoming direction of SmKS waves provides an additional diagnostic as to the origin of travel time anomalies. Here we use arrays of seismometers to measure travel time and direction anomalies of SmKS waves that sample the uppermost outer core. We form subarrays of EarthScope's regional Transportable Array stations, thus measuring local variations in travel time and direction. We observe systematic lateral variations in both travel time and incoming wave direction, which cannot be explained by changes to the radial seismic velocity profile of the outer core. Moreover, we find a correlation between incoming wave direction and travel time anomaly, suggesting that observed travel time anomalies may be caused, at least in part, by changes to the wave path and not solely by perturbations in outer core velocity. Modelling of 1-D ray and 3-D wave propagation in global 3-D tomographic models of mantle velocity anomalies match the trend of the observed travel time anomalies. Overall, we demonstrate that observed SmKS travel time anomalies may have a significant contribution from 3-D mantle structure, and not solely from outer core structure.
Laser interferometry enables to remotely measure microscopical length changes of deployed telecommunication cables originating from earthquakes. Long reach and compatibility with data transmission make it attractive for the exploration of both remote regions and highly-populated areas where optical networks are pervasive. However, interpretation of its response still suffers from a limited number of available datasets. We systematically analyze 1.5 years of acquisitions on a land-based telecommunication cable in comparison to co-located seismometers, with successful detection of events in a broad magnitude range, including very weak ones. We determine relations between a cable’s detection probability and the events magnitude and distance, introducing spectral analysis of fiber data as a tool to investigate earthquake dynamics. Our results reveal that quantitative analysis is possible, confirming applicability of this technique both for the global monitoring of our planet and the daily seismicity monitoring of populated areas, in perspective exploitable for civilian protection.
On the 6th of February 2023, a large magnitude earthquake (Pazarcık earthquake), $$M_{w}=$$ M w = 7.7, occurred in southeast Türkiye, which caused significant destruction in Türkiye and Syria. Relatively large magnitude aftershocks followed the main shock, and after 9 hours of the main event, another large magnitude earthquake (Elbistan earthquake) occurred, $$M_{w}=$$ M w = 7.6, on a nearby fault. This study analyzes the near-fault seismic signals from earthquakes larger than 5.5 recorded between the main shock and the 31st of March 2023. More than 60 impulsive motions are detected in 3 earthquakes, mostly concentrated in the Pazarcık and Elbistan earthquakes. In the Pazarcık earthquake, many impulsive motions are recorded in near-fault stations with periods of up to 14 s. In contrast, in the Elbistan earthquake, impulsive motions are spatially distributed, with pulse periods of up to 11 s and at distances greater than 150 km. Pulse periods mostly correlate with the magnitude of the earthquake, but pulse probability models do not predict impulsive motions over long distances. The presence of strong impulsive motions in vertical components is also observed. For both earthquakes, peak ground velocities (PGVs) are larger than predicted by ground motion prediction equations. The observation of long-period, large amplitude signals may indicate the presence of a directivity effect for both earthquakes. In some stations, spectral periods exceed the 2018 Turkish building design codes for long periods ( $$\ge$$ ≥ 1 s).
The receiver function (RF) method is the most widely adopted method for imaging crustal structures using earthquake data. Through attenuation during long‐distance propagation, high‐frequency components are scarce in teleseismic waveforms, resulting in low‐frequency RFs and low‐resolution crustal images. The Pn‐wave contains more high‐frequency components because of the short epicentral distance. To improve the resolution of crustal structure studies, we propose the Pn‐wave receiver function (PnRF) method. Unlike other near‐earthquake phases, the Pn‐wave can be considered a plane wave in the crust beneath seismic stations, and interference from other phases can be avoided at epicentral distances of 5–15°. PnRFs calculated from both numerical synthetic data and observational data at broadband seismic stations show that all converted waves are present in PnRFs at the predicted time according to the theory of plane waves. PnRFs calculated by observational data of a dense nodal array clearly show not only the converted wave from the Moho but also the converted wave from the crustal interface, which is too weak to be observed in tele‐RFs because the Pn‐wave has a larger incident angle and higher frequency than the teleseismic P‐wave. When used in conjunction with dense nodal array observations, the PnRF method has the potential to image crustal structures with a high resolution close to that of the deep seismic reflection method.
The southern Mariana margin is a tectonically distinctive and rapidly deforming region with the world deepest trench and unusual deformation and magmatism. However, its related deep structure and dynamics are still poorly understood. In this study, we determine robust 3-D P and S wave velocity tomography down to 130 km depth beneath the southern Mariana margin by using arrival-time data of local earthquakes recorded at 12 near-field stations. Our tomographic results together with local seismicity and focal mechanisms reveal that the subducted Pacific slab is rapidly rolling back with a steep dip angle and narrowly but strongly coupled with the thin forearc block, which result in the deepest trench. An inferred eastward mantle flow transports the enhanced hydrous mantle melt beneath the southwest Mariana rift to the southern Mariana Trough, causing unusual deformation, magmatism and volcanism in the new oceanic crust. In addition, seismicity in the west Mariana ridge lithosphere may indicate that active foundering of the arc lower crust is taking place there.
The International Data Centre (IDC) routinely applies event screening using a multi-technology approach in order to enable member states to characterize events as either natural or anthropogenic. Various event discriminants are presented in literature. At the Kenya National Data Centre (KE-NDC or N090), a systematic and step-by-step procedure of SEISMIC events discrimination is applied. Results from the discriminants adopted are obtained within a short time and the discriminants are relatively easy and fast to use. The discriminants used at KE-NDC (N090) are ranked in a hierarchy based on results obtained from one discriminant being applied in subsequent discriminants and ease of returning results within the shortest time possible to allow for events discrimination and dissemination of results. The discriminants applied and their hierarchy at KE-NDC include: (i) event location (epicenter/hypocenter parameters) (ii) hypocenter parameters based on events relocation using HYPOCENTER, (iii) magnitude determination, (iii) mb:Ms criteria and (iv) focal mechanism determination. Two seismic events are used as case examples to demonstrate how event discrimination is achieved based on the discriminants presented herein. The two seismic events are the 20190324 and 20200503 seismic events in southwestern and northern Kenya respectively. The choice of these two events is based on the fact that they were strong enough to be recorded by a number of global seismic stations and their magnitudes are comparable to the 2009, 2013 and 2016, but slightly lower than the 20,170,903, DPRK announced tests. Based on the discriminants used and presented herein, the two seismic events were categorized as being due to natural earthquakes.
The physical mechanisms controlling deep-focus earthquakes, or those observed at depths greater than 300 km, remain enigmatic. The leading processes by which deep-focus earthquakes are thought to occur include transformational faulting, thermal runaway and dehydration embrittlement, but distinguishing observations in support of one or more prevailing mechanisms are needed. In this study, we use a modified back-projection method, data recorded by the Hi-net array in Japan and a 3-D velocity model to produce source images of 19 deep-focus earthquakes within the Izu-Bonin subduction zone. We find that the rupture properties and fault plane orientations of imaged events separate according to reported moment magnitude, indicating the distinct operation of two moment-dependent causal mechanisms of deep-focus earthquakes in this region. We discuss these results in the context of previous observational, laboratory and numerical studies and emphasize the importance of continued research to validate the dual-mechanism hypothesis both in and outside Izu-Bonin. Such work may not only improve our understanding of the nucleation and propagation of deep-focus earthquakes, but also help clarify slab structure and subduction zone dynamics.
Accurate seismic phase detection and onset picking are fundamental to seismological studies. Supervised deep-learning phase pickers have shown promise with excellent performance on land seismic data. Although it may be acceptable to apply them to Ocean Bottom Seismometer (OBS) data that are indispensable for studying ocean regions, they suffer from a significant performance drop. In this study, we develop a generalized transfer-learned OBS phase picker—OBSTransformer, based on automated labelling and transfer learning. First, we compile a comprehensive data set of catalogued earthquakes recorded by 423 OBSs from 11 temporary deployments worldwide. Through automated processes, we label the P and S phases of these earthquakes by analysing the consistency of at least three arrivals from four widely used machine learning pickers (EQTransformer, PhaseNet, Generalized Phase Detection and PickNet), as well as the Akaike Information Criterion (AIC) picker. This results in an inclusive OBS data set containing ∼36 000 earthquake samples. Subsequently, we use this data set for transfer learning and utilize a well-trained land machine learning model—EQTransformer as our base model. Moreover, we extract 25 000 OBS noise samples from the same OBS networks using the Kurtosis method, which are then used for model training alongside the labelled earthquake samples. Using three groups of test data sets at subglobal, regional and local scales, we demonstrate that OBSTransformer outperforms EQTransformer. Particularly, the P and S recall rates at large distances (>200 km) are increased by 68 and 76 per cent, respectively. Our extensive tests and comparisons demonstrate that OBSTransformer is less dependent on the detection/picking thresholds and is more robust to noise levels.
An attempt was made to assess the quality of the International Data Centre (IDC) Reviewed Event Bulletin (REB) by comparing it with the Reviewed bulletin of the International Seismological Centre (ISC). To accomplish the task of comparison, the ISC Reviewed Bulletin events as downloaded from the ISC Web page for the month of October 2020 were used. The corresponding REB events as listed in the ISC bulletin were considered. During this period, a total of 3431 and 2652 (excluding 39 Infrasound events) events were considered for ISC and IDC bulletins, respectively. The comparison was performed using the information given in the header lines of the ISC bulletin from which matched and unmatched events could be extracted. The results showed that a total of 2315 events could be matched between the two bulletins. The percentage of matched events with relative location difference (D) < 1° was about 95.3% while the percentage of events with D ≥ 5o was about 0.35%. There were two potential events with IDC magnitude (mb) ≥ 4.0 and D ≥ 5°. The percentage of matched events with intersecting error ellipses was about 75.5%. Some results obtained from earlier studies which were produced by using similar approaches were also used in this study. In general, the results obtained in this study show that there was a slight difference when compared to the earlier comparison results.
The rupture behavior of intermediate-depth earthquakes in southern Java remains poorly understood despite their potential seismic hazard. In this study, we performed finite-fault inversions to investigate the rupture processes and source characteristics of five intermediate-depth earthquakes (60–300 km depth) with moment magnitudes
≥ 6.1 from 1998 to 2017 in the southern region of Java and its surrounding areas. Utilizing teleseismic body waves and surface waves, we employed a wavelet-based seismic inversion technique. Initially, we conducted preliminary inversions of the focal mechanisms (strike and dip) from the Global Centroid Moment Tensor (GCMT) database to determine the optimal fault plane orientation for slip distributions and source time functions (STFs). Our findings reveal that most of the earthquakes exhibited a simple rupture process characterized by a single and compact asperity with a single triangular STF, except for the 1998 earthquake. The results indicate that the ruptures primarily propagated unilaterally along the down-dip direction, except for the 2014 earthquake. We further analyzed the data incorporating directivity, which confirmed the rupture behavior. Three events suggested that the preferred rupture planes were near-vertical (down-dip), while two events exhibited subhorizontal orientations. Considering the challenges in determining the rupture plane associated with the subducting slab, the densely deployed national seismic networks in Java are expected to provide valuable insights into the dynamics of the subduction zone. By elucidating the source characteristics and rupture behavior of these intermediate-depth events, our study offers valuable insights for future seismic hazard assessments, particularly for densely populated regions of Java, Indonesia.
Earthquake activities in areas across the Midland basin and the Central Basin Platform of West Texas have significantly increased since mid‐2019 because of continuing industrial activities involving wastewater injection. The induced seismicity has allowed us to discover previously unknown seismogenic structures. This article presents a study focusing on seismotectonic characteristics of the Midland basin. For this purpose, we first delineated seismicity to identify seismogenic structures. In addition, we performed waveform moment tensor inversion to determine earthquake source mechanisms; subsequently, we inverted for the regional stress field using the obtained source mechanisms. As a result, we have obtained 150 focal mechanisms (from 2017 to November 2023). Based on the seismicity distribution and source mechanism patterns, we have identified 15 distinctive seismogenic zones. A vast majority of seismicity are located in the crystalline basement. Most of the 15 seismicity zones contain seismogenic structures commonly presenting linear geometry but with various orientation. Although the inverted focal mechanisms are a mix of strike‐slip and normal faulting, the inverted stress field contains the least compression axes (S3) commonly oriented in 330° azimuth across the 15 identified seismogenic zones. A combination of all seismogenic features has demonstrated that the Midland basin contains fault architectures resulting from the latest extensional tectonic activities, creating a series of basement‐rooted strike‐slip and normal faults. The two types of basement‐rooted faults coexist in our study area, where a presumed basement‐rooted rift system transects the Midland basin. They are reactivated by the current fluid injection.
To understand the seismic hazard of a subduction zone, it is necessary to know the geometry, location, and mechanical characteristics of the interplate boundary below which an oceanic plate is thrust downward. By considering the azimuthal dependence of converted P-to-S (Ps) amplitudes in receiver functions (RFs), we have detected the interplate boundary in the Makran subduction zone, revealing significant seismic anisotropy at the base of the accretionary wedge above the slab before it bends down beneath the Jaz Murian basin. This anisotropic feature aligns with a zone of reduced seismic velocity and a high primary/secondary wave velocity ratio (Vp/Vs), as documented in previous studies. The presence of this low-velocity highly anisotropic layer at the base of the accretionary wedge, likely representing a low-strength shear zone, could possibly explain the unusually wide accretionary wedge in Makran. Additionally, it may impact the location and width of the locked zone along the interplate boundary.
Accurate sensor orientation is important in providing reliable data used for seismological analysis such as P-wave receiver function analysis, shear-wave splitting, and ambient noise analysis. In this study, we used three distinct P-wave and Rayleigh-wave polarization analysis methods to estimate actual sensor orientation of 660 stations from CHINArray-II in northeastern margin of Tibetan plateau. We found that ∼42.12%–45.76% of the stations are well oriented with the absolute misorientation angle <3°, 42.42%–45.45% of the stations are fairly oriented with the absolute misorientation angle ranging from 3° to 10°, and 8.94%–11.82% of the stations are oriented with the absolute misorientation angle >10°. We further compared the results of some seismological analyses before and after sensor misorientation correction, such as Rayleigh-wave ellipticity (horizontal-to-vertical ratio) and P-wave receiver functions analysis. We found that when the sensor misorientation angle is large, it may lead to incorrect seismological results. With the same sensor misorientation, its influence on different seismological analysis is also different.
Following the 2004 Sumatra-Andaman earthquake (M 9.1), local earthquake occurrences in Southern Thailand has been actively observed to gain insight into their spatial distribution and magnitude variation. This is particularly important in relation to two major fault zones that have been reactivated, the Khlong Marui and Ranong Fault Zones, which were previously thought to be dormant. As many as 221 local earthquakes that occurred between 2005 and 2020 were gathered for this study using the observations on local, national, and international networks. Using SEISAN software, digital seismograms of 174 local events captured by at least three local seismic stations were analyzed. The results of this study show that the local earthquake epicenters are scattered spatially in some onshore areas of Southern Thailand and offshore throughout the Andaman Sea and Gulf of Thailand. Majority of the local earthquakes occured within and adjacent areas of the two main fault zones, hence the main sources of local seismicity. Nearly all of the events at hypocenters, which have depths ranging from 1.0 km to 78.4 km, are classified as shallow earthquakes. In terms of magnitude, the range of moment magnitude values is -0.1 ≤ Mw ≤ 5.0. This study was complemented by GPS data to observe the crustal deformation in the region. This study also shows that Southern Thailand's seismicity and crustal deformation were significantly impacted by a number of significant regional earthquakes. This study might leads to a re-evaluation of the seismic hazards for Southern Thailand.
The Sichuan–Yunnan block is located at the southeastern margin of the Tibetan Plateau, which is the key area as a transition belt from the active plate extrusion zone to the stable Yangtze Craton. Using a semiautomatic measuring method based on a graphical interface, we pick 81,585 precise travel times from 449 local earthquake records and finally obtain a crustal 3D P-wave velocity model of the Sichuan–Yunnan block. The model reveals an unexpected velocity contrast between the shallower and deeper crusts. It is summarized as weakly perturbed low-velocity belts encircling a high-velocity zone in the upper crust and strongly perturbed low-velocity anomalies in the mid-lower crust, respectively. The weak low-velocity anomalies are revealed along the major strike-slip faults, and their small perturbations may imply a slip-driven mechanism. The strong low-velocity anomalies are distributed extensively in the Sichuan–Yunnan block, and their great perturbations may be related to the partial melting of weak material extruded from Tibet. Besides, our result shows noticeable high-velocity anomalies in the core zone of the Emeishan Large Igneous Province (ELIP), which may be an indication of magma solidification from the ancient mantle plume. The result further exhibits an interesting pattern that the strong low-velocity anomalies are partially separated by the high-velocity anomalies in the ELIP. Such a specific pattern probably reflects that the stable zone in the ELIP leads to the bifurcation of weak Tibetan material.
Teleseismic receiver function (RF) analysis offers a passive-source analogue to detect impedance boundaries using the converted body waves generated by earthquakes. While the technique traditionally has targeted deep earth structures such as the Moho and transition zones, there is growing interest in assessing its applicability in basin-scale seismic characterization, ultimately aimed for onshore commercial integration as a cost-effective complement to existing active-source seismic surveys. Specifically, the conventional broadband seismometers used in global observational seismic experiments are not only logistically simple in terms of data acquisition, but they also record ground motions in three mutually orthogonal time series, enabling effective detection of shear waves and directional variations of observed signals. Here, we perform teleseismic RF analysis to detect shear-wave anisotropy and related symmetry axes orientations in a basin setting, using open-source seismic data recorded at 55 closely spaced seismic stations in the LaBarge Passive Seismic Experiment deployed in Wyoming between November 2008 and June 2009. We find that the strengths and geometry of the observed anisotropy are variable along the array. Significantly, not only can anisotropy effectively delineate subsurface fault interfaces, it can also substantiate and reveal additional interpretable signals that are otherwise disregarded. The estimated fast axes orientations compare favorably with the complex fracture systems documented in the region. Finally, we show that P-to-S amplitude variations with P incidence are systematic and modelable using existing computational tools, offering an opportunity to develop an analysis technique similar to amplitude variation with offset with the products of RF analysis.
Approximately 3300 shallow focus earthquakes and 1000 seismic stations have been used in a study of P wave travel times and station residuals, including azimuthal effects. The events were selected from a catalog containing 160,000 earthquakes, and those having uniform distance and azimuthal coverage were systematically relocated and used to refine P wave travel times and station corrections. Station corrections are provided for 994 seismic stations. The station corrections involve three terms: the static effect and two cosine terms with appropriate phase shifts. They exhibit general consistency over broad geographic areas and, where coverage is dense, often show abrupt changes from one geological province to another. The cos2theta terms appear to be due to upper mantle anisotropy, and they correlate with the stress direction in the crust.
A method of tomographic inversion to obtain three-dimensional velocity perturbations in the Earth's whole mantle has been developed, and applied to more than two million P-wave arrival time data reported by International Seismology Center (ISC). The model is parameterized with 32,768 blocks; the divisions in latitude, longitude, and radius are 32, 64, and 16, respectively. Horizontal cell size is 5.6° × 5.6°. The layer thicknesses vary with depth; 29 km just below the surface and 334 km just above the core-mantle boundary. Starting from a spherically symmetric Earth model, we obtained a three-dimensional model using the following iterative procedures. First, we relocated all the events; second, we backprojected the residual into the whole mantle; third, we refined the spherically symmetric Earth model. The solutions have been converged in five iterations. We adopted the following techniques in the backprojection procedure. The first order smoothness was introduced as a damping, which makes the solution independent of the starting model and its apparent fluctuation minimal. The basic equations for delay times and smoothness are solved using the conjugate gradient method, an iterative method which guarantees the convergence of solution into the exact least squares solution. The weight on the smoothness, i.e., the damping factor, was objectively determined by a simplified cross validation technique. The final solution was obtained as an average of the ten solutions, each of which was derived from one tenth of the total data set. The reliability of the solution is examined in two ways: (1) mapping the resolution given by the reconstruction of checkerboard patterns, and (2) mapping the variance given from the gaussian noise input.
An algorithm for calculating travel-time and amplitude curves of P waves by the ray theory is described in [1]. The earth model was a layered sphere. The dependence of velocity v upon depth r in each layer was represented by a cubical parabola. This approximation makes v(r) smooth enough to justify use of the ray theory (with the exception of regions where the ray theory is entirely inapplicable: caustics and shadow zones). The disadvantage of this approximation is that the travel-time curve (travel times τ (i0) and epicentral distances, Δ(i0)) is calculated by numerical integration, while the amplitudes are found by numerical differentiation of the travel-time curve.
At the U. S. Coast and Geodetic Survey, where preliminary earthquake locations must be computed from as many as 30,000 initially unrelated P arrivals and associated phases per month, considerable effort has been devoted toward making this process more fully automatic. A single pass program, COAST, has now been developed for use on the IBM 7030 (STRETCH) computer. This program discriminates compatible time groups from an uncorrelated chronological data file, computes a first approximation to the hypocenter using only five stations, and determines the refined hypocenter and earthquake magnitude using all relevant data without any intervention by a seismologist.
The usual methods of interpolating velocity-depth profiles cause discontinuities in the velocity gradient and anomalous geometrical ray amplitudes. Numerical methods are presented for interpolating a velocity profile and evaluating the ray integrals which avoid these difficulties. They allow smooth amplitude curves to be cal-culated directly. An example is given for the Herrin P velocity profile.
Soviet seismologists have published descriptions of 96 nuclear explosions conducted from 1961 through 1972 at the Semipalatinsk test site, in Kazakhstan, central Asia [Bocharov et al., 1989]. With the exception of releasing news about some of their peaceful nuclear explosions (PNEs) the Soviets have never before published such a body of information.
To estimate the seismic yield of a nuclear explosion it is necessary to obtain a calibrated magnitude‐yield relationship based on events with known yields and with a consistent set of seismic magnitudes. U.S. estimation of Soviet test yields has been done through application of relationships to the Soviet sites based on the U.S. experience at the Nevada Test Site (NTS), making some correction for differences due to attenuation and near‐source coupling of seismic waves.
Observations of P and S from deep earthquakes in the Hindu Kush region are analysed. They are reduced to a surface focus by a method of S. Mohorovičić. Cubic forms in Δ are found to fit the times of P satisfactorily up to 19° and of S to 21°. The coefficient of the cube term is less for S than for P, indicating that the S rays are much straighter than the P ones.
A cubic from 21° to 37° and a quadratic from 37° to 95° fitted the times of P, with t and dt/dΔ continuous. Beyond 92° it seems that the time curve becomes nearly straight, as had been suspected previously. For S cubics from 22.5° to 37° and from 37° to 94° fitted; there are few data beyond 95° and a linear extrapolation was made to 105°.
For both P and S there are considerable drops in dt/dΔ about distance 20°. Analysis for P at 1° intervals showed that the times beyond 20° vary smoothly with distance, and that the 20° discontinuity cannot be smoothed over more than 2°. The large amplitudes in this range strongly suggest that the variation of dt/dΔ is continuous and not due to the entry of an overtaking branch. The data for S are less clear but would suggest a similar strong d²t/dΔ² about 22°.
There is evidence that the times of P, extrapolated to distance 0°, are about 0.6 s more than those found by Willmore in the Heligoland explosion. The intervals between P and its near reflexion agree with this, and could be interpreted as an effect of the height of the region. If so it may be desirable at some stage to adapt the results to sea level.
New travel time tables to locate earthquakes are being developed under the Subcommission on Earthquake Algorithms of the International Association of Seismology and the Physics of the Earth's Interior (IASPEI).
The standard travel time tables used by seismological agencies such as the National Earthquake Information Center in Golden, Colo., and the International Seismological Centre (ISC) in Newbury, U.K., are the Jeffreys and Bullen tables published in 1940. These tables were developed 1930–1939 based on available observations, when station time keeping was frequently not reliable. Although the limitations of these tables have been recognized, no other tables provide such a complete representation of P, S and core phases.
The reverberative interval of the seismogram, defined as the portion following the surface wave train propagating along the minor arc and ending with the first body wave arrivals from the major arc, provides an excellent window in which to observe reflections from mantle discontinuities. On an SH-polarized seismogram in the intervals between ScSn and sScSn wave groups (zeroth-order reverberations) are approximately 15 min long and consist almost entirely of waves reflected one or more times from mantle discontinuities (first- and higher-order reverberations). We have developed signal enhancement and waveform inversion schemes to progressively extract information pertaining to mantle layering from the waveforms of zeroth- and first-order reverberations and have applied them to a data set of long-period digital seismograms drawn from a number of tectonic regions in and around the western Pacific. The results place important constraints on the nature of the transition zone discontinuities. -from Authors
Short-period waveform data were modeled in an attempt to constrain the P and S velocity structure at the earth's inner core boundary (ICB). The data set consists of recordings from 10 events in the South Pacific, and the data selection criteria as well as the methods of analysis are designed to avoid problems with receiver response. These data are modeled using a calculation technique that facilitates the consideration of a wide variety of models for the ICB. Results suggest that Q(alpha) in the inner core has the frequency dependence proposed by Doornbos (1983). The data determine the P velocities above and below the ICB to within a trade-off that is well constrained by the data. For example, with a P velocity structure above the ICB given by the PREM, the P velocity below the ICB is 11.03 + or - 0.03km/sec.
A large data set consisting of about 1000 normal mode periods, 500 summary travel time observations, 100 normal mode Q values, mass and moment of inertia have been inverted to obtain the radial distribution of elastic properties, Q values and density in the Earth's interior. The data set was supplemented with a special study of 12 years of ISC phase data which yielded an additional 1.75 × 10^6 travel time observations for P and S waves. In order to obtain satisfactory agreement with the entire data set we were required to take into account anelastic dispersion. The introduction of transverse isotropy into the outer 220 km of the mantle was required in order to satisfy the shorter period fundamental toroidal and spheroidal modes. This anisotropy also improved the fit of the larger data set. The horizontal and vertical velocities in the upper mantle differ by 2–4%, both for P and S waves. The mantle below 220 km is not required to be anisotropic. Mantle Rayleigh waves are surprisingly sensitive to compressional velocity in the upper mantle. High S_n velocities, low P_n velocities and a pronounced low-velocity zone are features of most global inversion models that are suppressed when anisotropy is allowed for in the inversion.
The Preliminary Reference Earth Model, PREM, and auxiliary tables showing fits to the data are presented.
We present a set of three parametric earth models (PEM) in which radial variations of the density and velocities are represented by piecewise continuous analytical functions of radius (polynomials of order not higher than the third). While all three models are identical below a depth of 420 km, models PEM-O and PEM-C are designed to reflect the different properties of the oceanic and continental upper mantles, respectively. The third model PEM-A is a representation of an average earth.The data used in inversion consist of observations of eigenperiods for 1064 normal modes, 246 travel times of body waves for five different phases and regional surface-wave dispersion data extending to periods as short as 20 seconds. Agreement of the functionals derived for the PEM models with the appropriate observations is satisfactory. In particular, the fit of free-oscillation data is comparable to that obtained in inversion studies in which constraints imposed on the smoothness of structure were not as severe as in our study.Our density distribution for all depths greater than 670 km is consistent with the Adams-Williamson equation to within 0.2% maximum deviation, and these minute departures result only from the limitations imposed by the parametric simplicity of our models. We also show that the velocities in the lower mantle are consistent with the complete third-order finite-strain theory to within 0.2% for VP and 0.4% for VS (r.m.s. relative deviations). The derived pressure derivatives of the velocities are very similar to those obtained for corundum structures in laboratory experiments.We conclude that any departures from homogeneity and adiabaticity within the inner core, outer core or lower mantle must be very small, and that introduction of such deviations is not necessary on the basis of the available observational evidence.
Thesis (Ph. D.)--University of California, San Diego, 1989. Includes bibliographical references (p. 323-331). Photocopy.
S and SKS travel times for arc distances of 30-126 degrees
Tests of seismic travel-time tables with well constrained hypocentres of earthquakes and explosions
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iasp91 600 k m source
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40. 60.
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Delta deg
Spherically symmetric Pand S-wave velocity models derived from ISC travel times, Abstracts 25th General Assembly IASPEI
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- K. Toy
Proceedings of the 4th Workshop on the European Geotraverse Project
- A. Zielhuis
A shear velocity model for Europe from ISC delay times
- A. Zielhuis
Characteristics of 96 underground nuclear explosions at the Semipalatinsk test site
- V. S. Bocharov
- A. Zelentsev
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P- and S-wave lower-mantle and core seismic velocity models and station corrections from ISC travel time data
- K. Toy