Eric Robert Engdahl

University of Colorado Boulder | CUB · Department of Physics

We produced a globally distributed catalog of earthquakes and nuclear explosions with calibrated hypocenters, referred to as the Global Catalog of Calibrated Earthquake Locations (GCCEL). This dataset currently contains 18,782 events in 289 clusters with >3.2 million arrival times observed at 19,258 stations. The term “calibrated” refers to the pro...

28 We produced a globally distributed catalog of earthquakes and nuclear explosions with calibrated 29 hypocenters, referred to as the Global Catalog of Calibrated Earthquake Locations or GCCEL. 30 This dataset currently contains 15,627 events with more than 2.6M arrival times observed at 31 17,826 stations. The term "calibrated" refers to the prop...

The original EHB global seismicity dataset (Engdahl et al., 1998) has been widely applied in earth science studies. We now present the refined ISC-EHB catalog for the period 1964-2016 based on updated criteria for earthquake selection, processing and relocation described in Weston et al. (2018). The ISC-EHB which currently includes 170,550 is a set...

Abstract A data set of earthquake hypocenters and associated traveltime residuals for seismic phases recorded by seismograph stations globally is an essential starting point for most studies of global seismicity and Earth structure. Such data sets have been produced in various forms by national and international agencies since the beginning of inst...

We outline the work done to extend and improve the ISC-GEM Global Instrumental Earthquake Catalogue, a dataset which was first released in 2013 . In its first version (V1) the catalogue included global earthquakes selected according to time-dependent cut-off magnitudes: 7.5 and above between 1900 and 1918 (plus significant continental earthquakes 6...

We outline the work done to extend and improve the ISC-GEM Global Instrumental Earthquake Catalogue, which was first released in 2013 (Storchak et al., 2013, 2015). Due to time and resource limitations, version 1 (V1) of the ISC-GEM Catalogue included global earthquakes selected according to time dependent cut-off magnitudes between 1900 and 2009:...

The EHB Bulletin of hypocentres and associated travel-time residuals was originally developed with procedures described by Engdahl, Van der Hilst and Buland (1998) and currently ends in 2008. It is a widely used seismological dataset, which is now expanded and reconstructed, partly by exploiting updated procedures at the International Seismological...

We present the final results of a two-year project sponsored by the Global Earthquake Model (GEM) Foundation. The ISC-GEM global catalogue consists of some 19 thousand instrumentally recorded, moderate to large earthquakes, spanning 110 years of seismicity. We relocated all events in the catalogue using a two-tier approach. The EHB location methodo...

Moment magnitude (MW) determinations from the online GCMT Catalogue of seismic moment tensor solutions (GCMT Catalog, 2011) have provided the bulk of MW values in the ISC-GEM Global Instrumental Reference Earthquake Catalogue (1900-2009) for almost all moderate-to-large earthquakes occurring after 1975. This paper describes an effort to determine M...

This paper outlines the re-computation and compilation of the magnitudes now contained in the final ISC-GEM Reference Global Instrumental Earthquake Catalogue (1900-2009). The catalogue is available via the ISC website (www.isc.ac.uk/iscgem/) and lists in a comma separated format the location and magnitude parameters (with corresponding uncertainti...

In order to produce a new global reference earthquake catalogue based on instrumental data covering the last 100+ years of global earthquakes, we collected, digitized and processed an unprecedented amount of printed early instrumental seismological bulletins with fundamental parametric data for relocating and reassessing the magnitude of earthquake...

In this introductory article we give a general description of the ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009). We also provide the background for four further articles that describe the effort in collecting and digitizing parametric earthquake bulletin data as well as the methodologies developed to compute homogeneous earthquake pa...

The geometry, kinematics, and mode of back-arc extension along the Andaman Sea plate boundary are refined using a new set of significantly improved hypocenters, global centroid moment tensor (CMT) solutions, and high-resolution bathymetry. By applying cross-correlation and double-difference (DD) algorithms to regional and teleseismic waveforms and...

On November 4 1977, a magnitude Ms 6.7 (mb 5.7) shallow-focus thrust earthquake occurred in the vicinity of the Adak seismographic network in the central Aleutian island arc. The earthquake and its aftershock sequence occurred in an area that had not experienced a similar sequence since at least 1964. About 13 1/2 months before the main shock, the...

[1] Subduction zone earthquakes exhibit a wide spectrum of rupture times that reflect conditions on the megathrust fault. Tsunami earthquakes are examples of slower than expected ruptures that produce anomalously large tsunamis relative to the surface-wave magnitude. One model explaining tsunami earthquakes suggests slip within patches of low rigid...

What are the geodynamic processes that caused these deadly earthquakes? Why have these earthquakes caused so much damage? What are the key lessons that we have learned from these devastating earthquakes? Answers to these questions will significantly enhance not only our understanding of earthquake occurrence but also our ability to reduce seismic h...

We present a new tomographic model of the mantle in the area of the 2010 M8.8 Maule earthquake and surrounding regions. Increased ray coverage provided by the aftershock data allows us to image the detailed subducting slab structure in the mantle, from the region of flat slab subduction north of the Maule rupture to the area of overlapping rupture...

This report describes the ISC-GEM Global Instrumental Earthquake Catalogue (1900-2009) created on the request and with sponsorship from the GEM Foundation.  The ISC-GEM Global Instrumental Earthquake Catalogue (1900-2009) is a major step forward on the way to improve characterization of spatial distribution of seismicity, magnitude frequency relat...

The great Mw = 9.0 2011 Tohoku earthquake appears to have complex rupture characteristics, with slower rupture velocity during the early portion of the rupture and spatial variations in the radiation frequency content. These spatial and temporal variations suggest that the subduction zone fault has spatially varying friction conditions that led to...

High-precision teleseismic double-difference locations and focal mechanisms of aftershocks of the 2004 Mw 9.2 Sumatra-Andaman earthquake illuminate an active imbricate fault system in the accretionary prism offshore northern Sumatra. They reveal repeated failure of a shallow northeast-dipping thrust fault above the megathrust, which we interpret to...

S U M M A R Y We present a new tomographic model of the mantle in the area of the 2010 M8.8 Maule earthquake and surrounding regions. Increased ray coverage provided by the aftershock data allows us to image the detailed subducting slab structure in the mantle, from the region of flat slab subduction north of the Maule rupture to the area of overla...

There is a continuum of rupture timescales for subduction zone earthquakes, from geodetically observed slow slip, tsunami earthquakes, and earthquakes of typical rupture velocities. Tsunami earthquakes, those interplate events that produce an anomalously large tsunami relative to the surface wave magnitude and are deficient in high frequency radiat...

The great 2011 Mw 9.0 Tohoku earthquake ruptured a segment of the megathrust fault along the subduction zone offshore northern Honshu in a region where earthquakes of Mw ~7-8 are much more common. The rupture characteristics of 2011 event suggest that the earthquake rupture occurred at different speeds during the ~150 s slip, with lower rupture vel...

Various models for the generation of tsunami earthquakes have been proposed, including shallow earthquake slip through low strength materials. Because these physical fault conditions would likely affect other earthquakes in the same rupture zone, source properties of other events may provide a guide to locations of tsunami earthquakes. The 25 Octob...

We present the current status of our efforts to produce a set of homogeneous earthquake locations and improved focal depths towards the compilation of a Global Catalog of instrumentally recorded earthquakes that will be complete down to the lowest magnitude threshold possible on a global scale and for the time period considered. This project is cur...

We have extended the double-difference seismic tomography method to teleseismic distances with 3-D ray tracing conducted through nested regional-global velocity models and applied the method to relocate seismicity from the Sumatra-Andaman region before and after the great earthquakes of 2004 and 2005. We tested the algorithm's accuracy using both i...

Taking advantage of the increased ray coverage due to seismicity following the 2004 December and 2005 March great earthquakes, an improved iterative regional–global tomographic method was applied to the Sumatra–Andaman and adjacent regions to better constrain the 3-D mantle velocity heterogeneity in the region. Velocity and hypocentral parameters w...

Improved precision teleseismic earthquake locations in subduction zones are being used to better understand shallow megathrust frictional conditions and determine the global distribution of tsunami earthquakes. Most global teleseismic catalogs fail to accurately locate shallow subduction zone earthquakes, especially mid-magnitude events, leading to...

The Andaman Sea region in the Northeast Indian Ocean is characterized by a complex extensional back-arc basin, which connects the Sumatra Fault System in the south with the Sagaing fault in the north. The Andaman back-arc is generally classified as a convergent pull-apart basin (leaky-transform) rather than a typical extensional back-arc basin. Obl...

The seismic detection capability of individual seismic arrays of the International Monitoring System (IMS) is investigated by comparing detections reported by selected seismic arrays in the IMS network with catalogs from selected areas having dense local networks and low magnitude thresholds. The study has been focused on three areas, the Tehran, I...

Five years after the devastating 26 December, 2004 M 9.3 Sumatra-Andaman earthquake, regional and global seismic networks have recorded tens of thousands of aftershocks. We use bulletin data from the International Seismological Centre (ISC) and the National Earthquake Information Center (NEIC), and waveforms from IRIS, to relocate more than 20,000...

Some earthquakes generate anomalously large tsunami waves relative to their surface wave magnitudes (Ms). This class of events, known as tsunami earthquakes, is characterized by having a long rupture duration and low radiated energy at long periods. These earthquakes are relatively rare. There have been only 9 documented cases, including 2 in the J...

Tsunami earthquakes and other slow seismic processes have been noted in many subduction zones around the world. One such example is the Kurile-Kamchatka margin, where 2 tsunami earthquakes occurred in 1963 and 1975, producing generally slow rupture and larger tsunami than expected for the earthquake size (M 7.8 and 7.5 respectively). Various models...

The Sumatra-Andaman subduction zone presents a significant seismic hazard to Southeast Asia, as exemplified by the 2004, 2005, and 2007 great earthquakes occurring offshore Sumatra. However, investigations of seismicity associated with these events are limited by the large uncertainties associated with teleseismic location catalogs and by the pauci...

We are investigating the crustal and upper mantle structure of the region in central Asia bounded approximately by longitude 41-67 deg E and latitude 20-44 deg N by using in-country datasets of seismic phase arrival times, supplemented by ground truth datasets developed from our previous research efforts. We present the results of Pn tomography usi...

Carl Kisslinger, a geophysicist who furthered scientific and international understanding through tireless devotion to his field, died on 31 December 2008 at his home in Boulder, Colo. He was 82. Studying geophysics under J. B. Macelwane at Saint Louis University, in Missouri, Carl earned his bachelor's degree in 1947 after an interruption due to Wo...

Vision: The Comprehensive Test Ban Treaty (CTBT) is receiving renewed attention in the Obama administration, in light of this administration's long range objective of steering towards a nuclear weapon free world. While the current International Data Center (IDC) has successfully detected several low magnitude explosions, opportunities exist to furt...

We report the current status of our efforts to create a global catalog of instrumental seismicity that can be used as an authoritative source of earthquake locations, magnitudes and other associated parameters (source mechanisms, rupture areas, casualties, references, etc) in a wide range of geoscience and social science investigations. These effor...

More than 2000 instrumentally recorded earthquakes occurring in the Iran region during the period 1918- 2008 have been relocated using an advanced seismic location technique. Relocation sharpens the image of seismic activity in the region and - more importantly - significantly improves event focal depths. Iranian seismicity is largely a result of t...

The shallow M8.4 outer-rise earthquake of March 2, 1933 is the largest recorded event of its kind. It produced strong ground motions and tsunami waves along the coast of Honshu and more than 3000 fatalities. Kanamori [EPSL, 1971] showed that this event was a normal-faulting rupture with ~N-S-striking nodal planes and proposed that this event repres...

The inclusion of data from the 2004-2005 great earthquake sequences into the tomographic modeling of the Sumatra region has greatly improved our resolving ability and has illuminated several important tectonic features along the Sumatra and adjacent subduction zones. Single iteration results using a nested regional- global tomography method and rep...

New data provided by the 2004-2005 Sumatra-Andaman great earthquake sequences allow us to image with improved detail the P-wave velocity structure beneath Sumatra and adjacent regions. Below northern Sumatra, we find that the slab is folded at depth, exhibiting geometry similar to that of the volcanic arc and the trench at the surface. We speculate...

We present a multiple event location technique that is able to produce minimally biased (location accuracy of 5 km or better) events from a cluster of earthquakes, without relying on prior ground truth information or dense local seismograph networks. In the hybrid hypocentroidal decomposition and reciprocal cluster analysis (HDC-RCA) method, HDC de...

We are investigating the crustal and upper mantle structure of the Iran region using in-country data sets of seismic phase arrival times, supplemented by ground-truth data sets developed from our previous research efforts. Other data sets from global, regional, and national bulletins in the region are being integrated as well. The in-country data s...

Subduction of the Indian lithosphere under Eurasia plays an important role in the tectonic evolution of the Tibetan plateau and surrounding regions. To improve our knowledge of pertinent mantle structures through tomographic imaging we combine P-wave arrival time data from temporary arrays in Tibet and stations of the Chinese Seismograph Network wi...

1] We document our tomographic method and present a new global model of three-dimensional (3-D) variations in mantle P wave velocity. The model is parameterized by means of rectangular cells in latitude, longitude, and radius, the size of which adapts to sampling density by short-period (1 Hz) data. The largest single data source is ISC/NEIC data r...

1] A new three-dimensional seismic model and relocated regional seismicity are used to illuminate the great Sumatra-Andaman Islands earthquake of December 26, 2004. The earthquake initiated where the incoming Indian Plate lithosphere is warmest and the dip of the Wadati-Benioff zone is least steep along the subduction zone extending from the Andama...

A new model of the three-dimensional shear velocity structure of the Africa-Eurasia plate boundary is presented. The new model is derived by jointly inverting different types of seismic data. The two main sources of information are regional waveforms and teleseismic S wave arrival times. We show that it is possible to find a model that fit the diff...

We have relocated 2556 events that were reported in the bulletins of the International Seismological Summary (ISS) during the period 1960–1963 using the phase arrival time data listed in the bulletins. Parts of the data were already available in digital form, and the rest we obtained by scanning the printed bulletins and applying an optical charact...

We present tomography results for Indonesia, with emphasis on the Sumatra region, from the inversion of teleseismic arrival times for regional earthquakes occurring during the period 1918-2006 and global earthquakes occurring 1964-2006. The earthquake locations are well-constrained teleseismically by the Engdahl, van der Hilst, and Buland (EHB) met...

The Calabrian subduction zone, situated southeast of the Italian 'boot' in the Ionian Sea, is the latest manifestation of African-Eurasian plate interaction. This plate interaction has been remarkably dynamic since the Mesozoic, hosting episodes of mountain belt and volcanic arc formation including, for example, the Alpine, Carpathian and Apennine...

We have revised the size estimates, nucleation points, rupture areas and aftershock distributions of all the instrumentally recorded earthquakes with a seismic moment greater than or equal to 3.0E+28 dyne-cm, equivalent to a moment magnitude of 8.25. Re-analysis of these events was done in order for the United States Geological Survey (USGS) to pub...

On 5 September 2004, two major earthquakes of MW 7.2 and MW 7.3 (referred to as the foreshock and the mainshock hereafter) occurred close to the Nankai Trough in southwest Japan. This earthquake sequence is located within the subducting Philippine Sea plate (PHS) with an aftershock distribution that overlapped a portion of the source region of the...

Two tsunami earthquakes occurred in the Java subduction zone within the last 12 years, providing multiple well-recorded tsunami events for analysis. The June 2, 1994 Mw = 7.8 and July 17, 2006 Mw = 7.7 reverse mechanism earthquakes produced tsunami with locally large (>8 m) runups, were deficient in high frequency energy relative to long period rad...

This research has the goal of developing in-country data sets that can be used to improve ground-based monitoring capabilities in southern Asia, in particular the region bounded by 20-44 deg N and 41-67 deg E, by providing information needed to develop and test more accurate travel time models for seismic phases that propagate in the crust and uppe...

Double Benioff zones provide opportunities for insight into seismogenesis because the underlying mechanism must explain two layers of deep earthquakes and the separation between them. We characterize layer separation inside subducting plates with a coordinate rotation to calculate the slab-normal distribution of earthquakes. Benchmark tests on well...

We have created a comprehensive and self-consistent digital catalog of instrumental seismicity of the Andean region with uniformly computer-determined hypocenters and magnitudes reduced to a common scale. Earthquakes have been relocated by a teleseismic location method that uses recent accurate travel time tables, depth phases, and incorporates cor...

Travel times of seismic waves from teleseismically recorded events that occurred within the Adak Island region of the Central Aleutian Islands are used to constrain both the velocity structure of the region and the locations of events. It is found that the P-wave velocity within the descending lithosphere is approximately 7–8 per cent faster than t...

The M-w 9.0 2004 Sumatra-Andaman Islands and M-w 8.6 Nias Island great earthquake sequences have generated over 5000 catalog-reported earthquakes along similar to 1700 km of the Sumatra-Andaman and western Sunda regions. studies of prior regional seismicity have been limited to global catalog locations that often have poorly constrained epicenters...

Most prior studies of regional seismicity in the Andaman-Sumatra-Java subduction zones have been limited to global catalog hypocenters that often have poorly constrained epicenters and depths. More than 8000 teleseismically well-constrained earthquakes occurring along this subduction margin during the period 1918- 2006 are relocated with special at...

We present an extension of the double-difference (DD) local earthquake tomography algorithm to teleseismic scales and show initial results for the Andaman and Sunda subduction systems. The 2004 and 2005 great Sumatra earthquakes and the resulting aftershock sequences generated thousands of globally recorded events and illuminated the shallow seismo...

The Geological Survey of India, following the Mw 9.0 2004 Sumatra-Andaman Islands great earthquake, deployed six three-component short-period digital seismograph stations along islands of the Andaman-Nicobar region. The arrival time data from this temporary local network, for the period 6 January through 16 March 2005, are combined with arrival tim...

More than 2000 instrumentally recorded earthquakes occurring in the Iran region during the period 1918-2004 have been relocated and reassessed, with special attention to focal depth, using an advanced technique for 1-D earthquake location. A careful review of starting depths, association of teleseismic depth phases, and the effects of reading error...

The main objective of this three-year research project is to produce a quality-controlled global GTO-5 event set, accompanied with waveform and groomed arrival time data sets. Our efforts are directed toward developing and refining methodologies for generating new ground-truth(GT) events through multiple-event location analysis. To accomplish this...

New location features for possible implementation by the International Seismological Centre in its standard location procedures are tested using a set of 156 well-located and geographically well-distributed earthquakes and explosions. The tests are performed using the Engdahl et al. ([Engdahl, E.R., Van der Hilst, R.D., Buland, R.P., 1998. Global t...

In 1994, three shallow earthquakes of Mw~ 6 occurred close together on blind thrusts near Sefidabeh in eastern Iran. In an earlier study of the teleseismic waveforms, the geomorphology and the faulting in the epicentral region, it was suggested that these earthquakes were associated with the growth of a ridge above a blind thrust fault system, whos...

The 2004 Mw 9.0 Sumatra-Andaman earthquake initiated along the Andaman subduction zone, north of the last great Sumatra earthquake along the Sunda Trench in 1861. During the 2005 Mw 8.7 Banyak Islands earthquake, a portion of the 1861 rupture subsequently failed. The boundary between the 2004 and 2005 ruptures broadly coincides with local trench ro...

In subduction zones, inclined Wadati-Benioff zones of seismicity occur within the subducting lithosphere and thus can be used to examine the structure of downgoing slabs. A particularly detailed set of information about the slab can be obtained from Double Benioff Zones (DBZs), where two sub-parallel planes of seismicity are separated in depth by a...

We have obtained a global high-resolution P-wave velocity model for the crust and mantle by means of travel-time tomography. The data set consists of a subset of 420,000 well-located events from the ISC bulletins and NEIC data up to September 2004. The selection contains 18 million P travel-times and additionally 2 million core phases. Furthermore,...

We have combined local seismic network data and a groomed ISC/NEIC database of phase arrivals at regional and teleseismic distances to determine accurate hypocenters and origin times for 224 earthquakes that are clustered in three regions of India (Koyna, Chamoli-Uttarkashi and Kutch). Multiple event relocation of these clusters of events, combined...

We review seismicity along the Nicobar/Andaman plate boundary prior to the Mw=9 earthquake of 26 December 2004, with particular attention to reverse slip in the central and northern parts of the rupture zone 600-1300 km north from the epicenter. Slip is partitioned between convergence and strike-slip motion, which in the northern Andamans is assist...

The earthquake of 26 December 2004 was a thrust event that occurred at the interface between the Burma/Andaman Plate and the Indian Plate. We discuss the seismic and thermal structure of the upper mantle in the vicinity of this earthquake revealed by modeling broad-band surface wave dispersion. The upper mantle model is constructed on a 1 deg by 1...

Based on well-constrainted hypocenter information and focal mechanism solutions, Seno and Yamanaka (1996) identify two classes of outer-rise/near-trench (OR/NT) earthquakes: 1) Shallow tensional events and 2) Deeper compressional events. They indicate that subduction zones with compressional deep events (DCE) also tend to have double seismic zones...

In subduction zones, inclined Wadati-Benioff zones of seismicity occur within the subducting lithosphere, and thus can be used to examine the structure of downgoing slabs. A particularly detailed set of information about the slab can be obtained from curious Double Benioff Zones (DBZs), where two sub-parallel planes of seismicity are separated in d...

The principal objective of this study is to estimate the absolute travel-time path anomalies of regional seismic phases observed at the Norwegian Seismic Array (NORSAR) with respect to the Earth model AK135 and to determine their relationship to the Earth's three-dimensional structure. At least with respect to the large-scale features of the correc...

A database of seismic networks and stations, including their operational history, has been compiled from all sources. In particular, the name, coordinates and elevations of seismic stations that have operated or are presently operating in Iran, India and China have been compiled. Seismic stations that have a long history of reporting phase data hav...

A three-year consortium project, with members of Science Applications International Corp., University of Colorado at Boulder, Harvard University, Multimax Inc., Geophysical Institute of Israel, Western Services, and University of California at San Diego, was initiated in 2000 to improve locations and reduce uncertainties in the Middle East, North A...