Clifford Thurber

University of Wisconsin–Madison | UW · Department of Geoscience

Tectonic activity, geothermal fluids, and microseismic events (MSEs) tend to occur in similar locations as a result of spatiotemporal changes in the subsurface stress state. To quantify this association, we analyze data from a dense seismic array deployed at the San Emidio geothermal field, Nevada for 1 week in December 2016 to coincide with a 19.4...

To understand the stress controls on the occurrence of a multi-fault rupture, we estimated the crustal stress between April 2013 to December 2018, i.e., before and after the Mw7.8 Kaikōura earthquake that occurred in New Zealand on 13 November 2016. We used both the focal mechanism solutions from the temporary seismic networks and the GeoNet moment...

An ~8700 m fiber‐optic cable is installed in surface trenches at the Brady Hot Springs geothermal site in Nevada, USA. A distributed acoustic sensing (DAS) system is applied to use this fiber‐optic cable to record seismic ambient noise. Noise cross‐correlation functions (NCFs) of channel pairs on one linear DAS segment and on two in‐line DAS segmen...

We present an ambient noise tomographic study of the mid-crustal magmatic system in the Katmai area, Alaska. Using multi-component (vertical and radial) seismic records at 70 stations deployed at various times over 20 years, we construct corresponding cross-correlograms and extract ∼1010 Rayleigh-wave dispersion curves in the periods between 2 and...

Imaging silicic systems using geophysics is challenging because many interrelated factors (e.g., temperature, melt fraction, melt composition, geometry) can contribute to the measured geophysical anomaly. Joint interpretation of models from multiple geophysical methods can better constrain interpretations of the subsurface structure. Previously pub...

The Laguna del Maule volcanic field (LdMVF) in Chile, a rapidly inflating silicic volcanic system without historical eruption, is intersected by active regional faults. The LdMVF provides an opportunity to observe how faults influence, accommodate, or are driven by an actively deforming large silicic system. Here we use Compressed High Intensity Ra...

With substantial postglacial rhyolite eruptions and ongoing rapid uplift, the Laguna del Maule volcanic field in the southern Andes provides an exceptional opportunity to study the dynamics of an active silicic magmatic system. Using 4,093 P arrivals from 137 distant earthquakes recorded by 44 local stations over ∼2.25 years, we conduct teleseismic...

High seismicity rates in eastern Indonesia occur due to the complex interaction of several tectonic plates which resulted in two deadly, destructive earthquake sequences that occurred in Lombok Island and the city of Palu, Sulawesi in 2018. The first sequence began in July with an Mw 6.4 event near Lombok, culminating in an Mw 7.0 event eight days...

The great 2012 Mw 8.6 strike‐slip earthquake beneath the Wharton Basin generated a complex aftershock sequence that maps onto a system of conjugate faults. Analysis of high‐precision aftershock locations with improved depth constraint is used here to characterize the seismogenic limits of the oceanic lithosphere. The study presents teleseismic doub...

Hundreds of earthquakes were recorded during a nine‐month ocean bottom seismometer deployment surrounding Lō'ihi submarine volcano, Hawai'i. The 12‐station ocean bottom seismometer network widened the aperture of earthquake detection around the Big Island, allowing better constraints on the location of seismicity offshore Hawai'i. Although this dep...

Distributed acoustic sensing (DAS) is one recently developed seismic acquisition technique that is based on fiber-optic sensing. DAS provides dense spatial spacing that is useful to image shallow structure with surface waves. To test the feasibility of DAS in shallow structure imaging, the PoroTomo team conducted a DAS experiment with the vibroseis...

Plain Language Summary Earthquake locations are fundamental for understanding the physics of earthquakes, defining the orientations and geometries of faults that have slipped seismically, and assisting in seismic hazard forecasting and assessment. We have mapped the locations of approximately 2,700 of the largest aftershocks that followed the 14 No...

Knowledge of the shear wave velocity structure in the Parkfield, California region is a key factor for obtaining accurate earthquake locations and improving wave propagation simulations, but it has been poorly resolved in previous studies. We have conducted an ambient noise tomography study using continuous waveform data from available seismic stat...

The Laguna del Maule (LdM) volcanic field comprises the greatest concentration of postglacial rhyolite in the Andes and includes the products of ~40 km³ of explosive and effusive eruptions. Recent observations at LdM by interferometric synthetic aperture radar and global navigation satellite system geodesy have revealed inflation at rates exceeding...

We derive high-resolution P and S seismic velocities (VP and VS) within the South-Central Transverse Ranges section of the San Andreas Fault (SAF), using a new double-difference tomography algorithm incorporating both event-pair and station-pair differential times. The addition of station-pair data allows for better absolute event locations and hig...

Vp/Vs models provide important complementary information to Vp and Vs models, relevant to lithology, rock damage, partial melting, water saturation, etc. However, seismic tomography using body wave traveltime data from local or regional earthquakes does not constrain Vp/Vs well due to the different resolution of Vp and Vs models, with the Vp models...

We deployed a dense seismic array to image the shallow structure in the injection area of the Brady Hot Springs geothermal power plant in western Nevada. The array was composed of 238 three-component, 5 Hz nodal instruments, 8700 m of distributed acoustic sensing (DAS) fiber-optic cable (FOC) installed horizontally in surface trenches, and 400 m of...

We derive new Rayleigh wave group velocity models and a 3-D shear wave velocity model of the upper crust in the San Francisco Bay region using an adaptive grid ambient noise tomography algorithm and 6 months of continuous seismic data from 174 seismic stations from multiple networks. The resolution of the group velocity models is 0.1 ◦ –0.2 ◦ for s...

The PoroTomo research team deployed two arrays of seismic sensors in a natural laboratory at Brady Hot Springs, Nevada in March 2016. The 1500 m (length) × 500 m (width) × 400 m (depth) volume of the laboratory overlies a geothermal reservoir. The distributed acoustic sensing (DAS) array consisted of about 8400 m of fiber-optic cable in a shallow t...

The tectonics of the Sunda arc region is characterized by the junction of the Eurasian and Indo‐Australian tectonic plates, causing complex dynamics to take place. High‐seismicity rates in the Indonesian region occur due to the interaction between these tectonic plates. The availability of a denser network of seismometers after the earthquakes of M...

The Deep Fault Drilling Project (DFDP) on the central Alpine Fault, South Island, New Zealand, has motivated a broad range of geophysical and geological studies intended to characterize the fault system in the locality of the drill site at various scales. In order to better understand the structural features of the central Alpine Fault, we have dev...

We utilise seismic data from the central section of the Alpine Fault to locate earthquakes and image crustal structure in three dimensions. Tomography results from c. 6500 sources reveal the fault as either a southeast-dipping low-velocity zone or a marked velocity contrast in different parts of the study region. Where our model is best resolved, w...

Joint inversions of seismic data recover models that simultaneously fit multiple constraints while playing upon the strengths of each data type. Here, we jointly invert 14 years of local earthquake body wave arrival times from the Alaska Volcano Observatory catalog and Rayleigh wave dispersion curves based upon ambient noise measurements for local...

Explosive eruptions of large-volume rhyolitic magma systems are common in the geologic record and pose a major potential threat to society. Unlike other natural hazards, such as earth-quakes and tsunamis, a large rhyolitic volcano may provide warning signs long before a caldera-forming eruption occurs. Yet, these signs—and what they imply about mag...

We obtain 3D Q(P) and Q(S) models for the Delta region of the Sacramento and San Joaquin rivers, a large fluvial-agricultural portion of the Great Valley located between the Sierra Nevada batholith and the San Francisco Bay-Coast Ranges region of active faulting. Path attenuation t* values have been obtained for P and S data from 124 distributed ea...

Okmok volcano is an active volcanic caldera located on the northeastern portion of Umnak Island in the Aleutian arc, with recent eruptions in 1997 and 2008. The Okmok area had ~900 locatable earthquakes between 2003 and June 2008, and an additional ~600 earthquakes from the beginning of the 2008 eruption to mid 2009, providing an adequate dataset f...

Double-difference seismic tomography can estimate velocity structure and event locations with high precision, but its high-computation cost along with large memory usage prevents the use of a personal computer to process very large datasets and requires a long-computation time. This work proposes graphics-processing-unit(GPU)-based acceleration sch...

We invert arrival time data from local earthquakes occurring between September 2004 and May 2009 to determine the three-dimensional (3D) upper crustal seismic structure in the Katmai volcanic region. Waveforms for the study come from the Alaska Volcano Observatory’s permanent network of 20 seismic stations in the area (predominantly single-componen...

We present a multiscale seismic tomography method incorporating differential time data. This is an extension of the double-difference tomography method to teleseismic distances using a nested regional-global model parameterization. It allows inclusion of absolute and differential time data observed at any distance, potentially improving resolution...

We incorporate body-wave arrival time and surface-wave dispersion data into a joint inversion for three-dimensional P-wave and S-wave velocity structure of the crust surrounding the site of the San Andreas Fault Observatory at Depth. The contributions of the two data types to the inversion are controlled by the relative weighting of the respective...

[1] A three-dimensional (3-D), high-resolution P-wave seismic attenuation model for the New Madrid Seismic Zone (NMSZ) is determined using P-wave path attenuation (t*) values of small-magnitude earthquakes (MD < 3.9). Events were recorded at 89 broadband and short period seismometers of the Cooperative New Madrid Seismic Zone Network and 40 short p...

Volcanoes are critical geologic hazards that challenge our ability to make long-term forecasts of their eruptive behaviors. They also have direct and indirect impacts on human lives and society. As is the case with many geologic phenomena, the time scales over which volcanoes evolve greatly exceed that of a human lifetime. On the other hand, the ti...

The Mw=7.1 Darfield (Canterbury) and Mw=6.2 Christchurch earthquakes and related aftershocks in Canterbury, New Zealand have revealed a major hazard in the Canterbury region in the form of the Greendale Fault and a number of associated faults. The strength of these apparently low slip-rate faults may affect the recurrence intervals of subsequent ea...

[1] Low-slip-rate regions often represent under-recognized hazards, and understanding the progression of seismicity when faults in such areas rupture will help us to better understand earthquake rupture patterns. The 3 September 2010 (UTC) Mw 7.1 Darfield earthquake revealed a formerly unrecognized set of faults in the Canterbury region of New Zeal...

The use of seismic noise interferometry to retrieve Green's functions and the analysis of volcanic tremor are both useful in studying volcano dynamics. Whereas seismic noise interferometry allows long-range extraction of interpretable signals from a relatively weak noise wavefield, the characterization of volcanic tremor often requires a dense seis...

We present a three-dimensional (3D) P wave velocity (Vp) model of the Parkfield region that utilizes existing P wave arrival time data, including fault zone head waves (FZHWs), and data from direct wave secondary arrivals (DWSAs). The first-arrival and DWSA travel times are obtained as the global-and local-minimum travel time paths, respectively. T...

[1] Kilauea Volcano, Hawaii, has hosted a long series of slow slip events observed since the installation of the continuous GPS network in 1996. Kilauea's slow slip events are inferred to occur on the decollement fault at 8 km depth beneath its south flank, with a location updip of the epicenters of large, regular earthquakes. Fault slip typically...

Parameter Estimation and Inverse Problems, 2e provides geoscience students and professionals with answers to common questions like how one can derive a physical model from a finite set of observations containing errors, and how one may determine the quality of such a model. This book takes on these fundamental and challenging problems, introducing...

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...

A novel approach is to use low cost launch space vehicle to deliver a network of large number of microsensors over an extended area of a body to observe multiple phenomena then transmit the data back to Earth through a relay system.

The first four months of aftershocks of the Darfield earthquake have been studied using data from temporary and permanent seismic stations to investigate the fault geometry, stress field and evolution of seismicity and seismic properties. Earthquake relocations illuminate fault segments and show that the majority of aftershocks occurred beyond the...

Efforts to determine general moment tensors (MTs) for microearthquakes in volcanic areas are often hampered by small seismic networks, which can lead to poorly constrained hypocentres and inadequate modelling of seismic velocity heterogeneity. In addition, noisy seismic signals can make it difficult to identify phase arrivals correctly for small ma...

We revisit the rupture zone of the 1989 Mw6.9 Loma Prieta earthquake, central California, by developing high-resolution three-dimensional (3-D)Vp and Vp/Vs models. We apply the simul2000 inversion method and algorithm to a set of "composite" events, which have greater number of picks per event and reduced random picking errors compared with traditi...

In order to understand the dynamics of volcanoes and to assess the associated hazards, the analysis of ambient seismic noise - a continuous passive source - has been used for both imaging and monitoring temporal changes in seismic velocity. Between pairs of seismic stations, surface wave Green's functions can be retrieved from the background ocean-...

The internal structure, loading processes, and effective boundary conditions of a volcano control the deformation observed at the Earth's surface. Using finite element models (FEMs), we simulate the response due to a pressurized magma chamber embedded in a domain having a distribution of elastic material properties. We present the Pinned Mesh Pertu...

Parameter Estimation and Inverse Problems, 2e provides geoscience students and professionals with answers to common questions like how one can derive a physical model from a finite set of observations containing errors, and how one may determine the quality of such a model. This book takes on these fundamental and challenging problems, introducing...

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...

Green's functions calculated with ambient seismic noise may aid in volcano research and monitoring. The continuous character of ambient seismic noise and hence of the reconstructed Green's functions has enabled measurements of short-term (~days) temporal perturbations in seismic velocities. Very small but clear velocity decreases prior to some volc...

Detailed P-wave speed velocity structure beneath the Sunda arc has been successfully imaged by applying a non-linear approach to seismic tomography. Nearly one million compressional phases from events within the Indonesian region have been used. These include the surface-reflected depth phases pP and pwP in order to improve the sampling of the uppe...

Several slow slip events have been observed on Kilauea volcano providing opportunities to look for concurrent tectonic tremor. Slow slip events have been observed to be accompanied by tectonic tremor in numerous subduction zones worldwide. The HVO seismic monitoring network recorded continuous waveforms during slow slip events in 1998, 2007, and 20...

Tectonic tremor is a weak but persistent shaking of the Earth that was first discovered in subduction zones and later found beneath the San Andreas Fault (SAF). Tremor events represent spasmodic slip on the deep extension of the SAF, occurring at a depth of about 20-25 kilometers. Tremor occurs deeper than the nearby regular earthquakes, which can...

Okmok Volcano is an active caldera located on Umnak Island in the Aleutian Island arc. Okmok, having recently erupted in 1997 and 2008, is well suited for multidisciplinary studies of magma migration and storage because it hosts a good seismic network and has been the subject of synthetic aperture radar (SAR) images that span the recent eruption cy...

Eastern California's Long Valley Caldera (LVC) and the Mono-Inyo Crater volcanic systems have been active for the past ~3.6 million years. Long Valley is known to produce very large silicic eruptions, the last of which resulted in the formation of a 17 km by 32 km wide, east-west trending caldera. Relatively recent unrest began between 1978-1980 wi...

The 7.2 Darfield earthquake arrived unexpectedly and produced a ground-surface fault rupture that extended for at least 29.5km. We seek to better understand the characteristics of these heretofore unknown fault/s and the surrounding area, namely: Seismicity; Poisson's ratio (related to fluid content, lithology, and fractures); Fast direction of ani...

The Sacramento-San Joaquin River Delta (SSJRD) occurs at the confluence of the Sacramento and San Joaquin rivers in the Central Valley of California. The Central Valley is a sedimentary basin that divides the granitic Sierra Nevada range on the east from the heterogeneous Franciscan formation to the west. It is home to a series of levees that contr...

Standard methods for mapping variations in seismic attenuation (Q) structure using local earthquake data involve a two-step process. First, values of the whole path attenuation operator t* are determined from earthquake data recorded on a seismic array by inverting observed spectra for source and attenuation parameters. Then, these t* data are used...

The Laguna del Maule (LdM) volcanic field of the Andean Southern Volcanic Zone extends over 500 square kilometers and comprises more than 130 individual vents. As described by Hildreth et al. (2010), the history has been defined from sixty-eight Ar/Ar and K-Ar dates. Silicic eruptions have occurred throughout the past 3.7 Ma, including welded ignim...

Dike intrusions alter the stress state within a volcano and thus not only deform the earth's surface but also commonly induce earthquake swarms. We seek to utilize deformation and seismicity to image time-dependent dike propagation. While geodetic observations are commonly used to constrain the overall geometry of dike intrusions, they often have l...

The Central American subduction zone exhibits a wide variability in along-arc slab hydration as indicated by geochemical studies. These studies generally show maximum slab contributions to magma beneath Nicaragua and minimum contributions beneath Costa Rica, while intermediate slab fluid contributions are found beneath El Salvador and Guatemala. Ge...

In 2008 the region of Trident and Novarupta volcanoes (TN) in the Katmai volcanic cluster, Alaska, experienced a swarm of small shallow earthquakes in association with a series of deep (>25 km) long-period (DLP) earthquakes. We captured the latter half of the swarm with a dense array of 10 temporary broadband seismometers deployed within the larger...

Seismic tomography with a non-linear approach has been successfully applied to image the P-wave velocity structure beneath the Banda arc in detail. Nearly one million compressional phases including the surface-reflected depth phases pP and pwP from events within the Indonesian region have been used. The depth phases have been incorporated in order...

Several studies of the 2004 Parkfield earthquake have linked the spatial distribution of the event’s aftershocks to the mainshock slip distribution on the fault. Using geodetic data, we find a model of coseismic slip for the 2004 Parkfield earthquake with the constraint that the edges of coseismic slip patches align with aftershocks. The constraint...

We incorporate 14 years of earthquake data from the Alaska Volcano Observatory with data from a 1975 controlled-source seismic experiment to obtain the three-dimensional P and S wave velocity structure and the first high-precision earthquake locations at Augustine Volcano to be calculated in a fully three-dimensional velocity model. Velocity tomogr...

The South Iceland Seismic Zone (SISZ) has exhibited several textbook examples of migrating seismicity. Sequences of earthquakes with main shock magnitudes of (at least) 6 have occurred there on at least three different occasions, beginning in 1784, 1896, and 2000. The seismicity appears to migrate from east to west with apparent speeds varying over...

Recent studies of slow earthquakes point to the involvement of high-pressure fluids near the plate boundary in the occurrence of slow earthquakes. Here, we show fine-scale variations of seismic velocities and converted teleseismic waves that reveal the presence of zones of high-pressure fluids released by progressive metamorphic dehydration reactio...

Alaska contains over 100 volcanoes, 21 of which have been active within the past 20 years, including Augustine in Cook Inlet, and Akutan and Makushin in the central Aleutian arc. We incorporate 14-15 years of earthquake data from the Alaska Volcano Observatory (AVO) to obtain P-wave velocity structure and high-precision earthquake locations at each...

Okmok Volcano is an active volcanic caldera located on the northeastern portion of Umnak Island in the Aleutian arc, and most recently erupted in 2008. We present updated results from Okmok seismicity between January 2003 and May 2009. The volcanic caldera has been well instrumented with a network of as many as nine short-period and four broadband...

Located 110 miles from Anchorage, Alaska, Redoubt Volcano is a significant hazard to the Cook Inlet region and overlying flight paths. The volcano has been continuously monitored by a 5 to 10-station seismic network since 1989. Previous work by DeShon et al. (2007) focused on reducing location errors of Redoubt earthquakes from 1989-2005 by computi...

Rifting occurs as episodes of active deformation in individual rift segments of the Northern Volcanic Zone (NVZ) in Iceland. Here we simulate deformation around the Krafla central volcano and rift system in NVZ in order to explain InSAR data acquired between 1993 and 1998. The General Inversion for Phase Technique (GIPhT) is used to model the InSAR...

The Sacramento-San Joaquin River Delta is a component of the major basins east of the California Coast Ranges, and it contains levees that may fail in major earthquakes. The largest magnitude earthquake sources may occur on Bay Area faults, over 50-km away from the Delta, and thus regional attenuation is important to consider. Regionally, long-term...