S. L. Bilek

New Mexico Institute of Mining and Technology | NMT · Department of Earth and Environmental Science

Increased seismicity in central New Mexico is associated with a midcrustal magma body underlying an extensional rift zone, with earthquakes typically occurring in spatially compact clusters with occasional swarms occurring within limited time periods. Seismic swarms are observed in a range of environments and can be indicative of a variety of geoph...

Tiltmeters have the potential to resolve ground deformation due to changes in hydraulic head induced by conduit pressurization. Conduit pressure variations cause groundwater to be stored or released from storage within the surrounding rock matrix. We modeled this process and infer whether the resulting deformation is measurable with tiltmeters and...

This study utilized ambient seismic noise tomography to investigate correlations of hydrogeological systems with heterogeneous porosity with the internal velocity structure of karst aquifers using the Floridan Aquifer System (FAS) as an example. We conducted a seismic signal analysis with 30 days of vertical component seismic data acquired within t...

Typical use of ambient noise interferometry focuses on longer period (>1 s) waves for exploration of subsurface structure and other applications, while very shallow structure and some environmental seismology applications may benefit from use of shorter period (<1 s) waves. We explore the potential for short‐period ambient noise interferometry to d...

The Cascadia subduction zone (CSZ) is known to host M9 megathrust ruptures; however, no such event has occurred in historical observation. The distribution and characteristics of small‐ to moderate‐sized earthquakes can be used to determine the behavior of the megathrust fault but are notably absent offshore the CSZ due to the distance from onshore...

Variations in subsurface flow processes through a karst aquifer that feeds Bear Spring in southeastern Minnesota were captured on a temporary seismic network during injection experiments and a natural recharge event. Each experiment involved injecting ∼13,000 L of water into an overflow spring, and the natural event was triggered by a large rainsto...

The purpose of this work is to gain insight into karst conduit-matrix fluid flow and anticipated solid deformational response that could inherently be optimized and field-tested via geodetic techniques. The objective is to perform a finite element modeling exercise founded on first-principal physics governing the coupling between fluid and solid me...

The advent of low-cost continuously recording cable-free autonomous seismographs, commonly referred to as nodes, enables dense spatiotemporal sampling of seismic wavefields. We create virtual source reflection profiles using P waves from five teleseis-mic events recorded by the Sevilleta node array experiment in the southern Albuquerque basin. The...

Data from an amphibious seismic network in Cascadia (northwest North America) provide unique near-source observations to assess the influence of subducting topography on seismicity. Using subspace detection, we detect and locate 222 events in two separate clusters, near a subducted seamount and a possibly accreted seamount. Seismicity in both clust...

The Raton Basin has the highest number of earthquakes in Colorado and New Mexico from 2008 to 2010. The rate of both wastewater injection and earthquakes in the Basin increased dramatically starting in 1999 and 2000, respectively. We compare seismicity (ML 0.0-4.3) in the Raton Basin from 2008 to 2010 with the location of modeled pore pressure incr...

Tsunami earthquakes, events that generate larger than expected tsunami and are deficient in high frequency seismic radiation, are rare but hazardous to coastal populations. One model for these events is shallow rupture through low strength materials. We calculate seismic moment, corner frequency, and stress drop for 216 earthquakes (2.1?<?Mw?<?4.7,...

We develop a catalog of small magnitude seismicity across Colorado and New Mexico from the Earthscope USArray Transportable Array/CREST seismic networks from 2008-2010 to characterize active deformation in the Rio Grande rift. We recorded over 800 earthquakes in the Rio Grande Rift region, not including induced earthquakes and mine blasts, and find...

Online Material: Table of station locations. Along the northwestern coast of North America, the Cascadia subduction zone (CSZ) produces a range of slip behavior along the plate boundary megathrust zone, from great earthquakes to episodic slow slip and tremor downdip of the seismogenic zone (e.g., Ghosh et al. , 2010, 2012; McCausland et al. , 2010...

Dynamic earthquake triggering, the process through which stresses transmitted through the passage of seismic waves can trigger remote faults to fail, has been shown to be fairly common throughout the globe and especially in seismically active areas of high heat flow and geothermal activity. We explore the possibility of dynamic earthquake triggerin...

[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...

The earliest documented records of large earthquakes in New Mexico go back to the early 1900s, and seismicity has been monitored instrumentally since the early 1960s. This catalog is a continuation of previous catalogs spanning 1962 through 2004 and includes 165 earthquakes Md ≥ 2.0. In addition it also includes all located events with Md ≥ 0 in Ne...

Among the wide range of thermal, petrologic, hydrological, and structural factors that potentially affect subduction earthquakes, the roughness of the subducting seafloor is among the most important. By reviewing seismic and geodetic studies of megathrust locking/creeping state, we find that creeping is the predominant mode of subduction in areas o...

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...

The geology near a seismic source has a major effect on seismic waves recorded at distance. This can be especially true in the case of man-made explosions, due to increased geologic heterogeneity at shallow depths and interactions with the free surface. Yucca Flat (YF), a sedimentary basin on the Nevada National Security Site, has hosted hundreds o...

The February 27, 2010 Maule earthquake (Mw 8.8) ruptured a ~600 km segment of the Chilean subduction zone just north of the 1960 rupture zone. Results from back-projection analysis of the mainshock suggest along-strike variation in the energy release, with low frequency, slow velocity slip along the southern end of the rupture. Thus, if these varia...

The release of energy during an earthquake changes the stress state and seismicity both locally and remotely. Far-field stress changes can lead to triggered earthquakes coinciding with the arrival of the surface waves. This dynamic triggering is found to occur in a variety of tectonic settings, but in particular magmatic regions. Here we test wheth...

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...

Seamount subduction is a common process in subduction zone tectonics. Contradicting a widely held expectation that subducting seamounts generate large earthquakes, seamounts subduct largely aseismically, producing numerous small earthquakes. On rare occasions when they do produce relatively large events, the ruptures tend to be complex, suggesting...

Oceanic plates vary in temperature, topography, and sediment load as they enter subduction zones. These variations persist along the subduction interface causing perturbations in coupling and earthquake rupture processes. We explore the effects of variable subducting plate structure on microseismicity rupture characteristics along the Nicoya Penins...

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...

The Mw = 7.8 1994 and the Mw = 7.7 2006 interplate thrust mechanism earthquakes that occurred in the Java subduction zone produced dominantly normal-faulting aftershocks, unusual for large megathrust main shocks. Various models proposed for these earthquake sequences invoke main shock rupture on an isolated portion of a decoupled plate boundary fau...

We compute apparent stress for 114 aftershocks (0.9≤ML≤ 3.7) of the 1999 Mw = 6.9 Quepos, Costa Rica, thrust-faulting earthquake to examine the influence of subducting plate topographic complexity near the Osa Peninsula on earthquake rupture. Using seismic coda techniques, we find a heterogeneous distribution in apparent stress of 0.1-2.5 MPa (mean...

Geodetically determined interseismic coupling variations have been found in subduction zones worldwide. These coupling variations have been linked to heterogeneities in interplate fault frictional conditions. These connections to fault friction imply that observed coupling variations are also important in influencing details in earthquake rupture b...

Earthquake swarms, often attributed to magma or fluid movement in the uppermost crust, have differing statistics depending on tectonic setting, with volcanic swarms producing b-values of up to 2.5 and continental rift swarms having b-values ∼0.8-1. Along the Rio Grande continental rift (RGR) in the western US, earthquake swarms have occurred in the...

Ocean floor bathymetric features such as seamounts and ridges are thought to influence the earthquake rupture process when they enter the subduction zone by causing changes in frictional conditions along the megathrust contact between the subducting and overriding plates. Once subducted, these features have been described as localized areas of hete...

Earthquakes along the shallow South American subduction zone exhibit heterogeneous rupture characteristics, going back several centuries of the earthquake record in this area. This heterogeneity is manifest in several ways, such as changes in rupture mode from magnitude > 8 events during one century followed by smaller ones in other time periods, a...

Subduction zones outline much of the Pacific plate, producing many of the largest and most destructive earthquakes recorded. Thus there is considerable interest in understanding the tectonics and dominant processes associated with these margins, as variations in these processes may be a factor in

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...

In general, the vast majority of global seismicity occurs within the upper 60 km of subduction zones. However, focused examination of earthquake locations within any given subduction zone shows a complex distribution, with high concentrations of seismicity adjacent to relatively quiet zones. In addition, there is a wide spectrum of earthquake ruptu...

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...

Earth structure plays an important role in the generation of seismic waves for all sources. Nowhere is this more evident than at near-surface depths where man-made sources, such as explosions, are conducted. For example, short-period Rayleigh waves (Rg) are excited and propagate in the upper 2 km of Earth's crust. The importance of Rg in the genera...

The Socorro Magma Body (SMB) is a mid-crustal, sill-like intrusion located at 19 km depth in central New Mexico that produces significant seismic activity relative to the rest of the state. Within this region, shallow earthquake swarms, <8 km depth, containing up to several hundred events each, occur over decadal time scales in an area approximatel...

Seismicity in central New Mexico, southwestern United States, is dominated by earthquakes occurring above the mid-crustal Socorro Magma Body (SMB). The SMB is a sill-like feature ≥ 3400 km2 in area, with a top surface at 19-km depth spanning the inner Rio Grande rift half-graben system. Inflation of the magma body at rates of several mm/year, perha...

The 25 March 1990 (Mw = 7.0) subduction megathrust earthquake that occurred offshore the Nicoya Peninsula, Costa Rica, produced a large number of aftershocks on the subduction plate interface as expected and preceded an unusual sequence of earthquakes 75 km inland that had two periods of significant increase, one at 60–90 days and one near 270 days...

Earthquake rupture processes may be influenced by the subduction of large topographic features. Features such as seamounts protrude from a subducting plate and may interact with the overriding plate to cause changes in normal stress due to differences in interplate coupling. Areas that are strongly coupled may accumulate more stress than areas that...

Subduction zones, home to the majority of the world's earthquakes, have also been the hosts for some of the world's most devastating tsunami. Seismic characteristics of subduction zone earthquakes, including the time constant of rupture, range from typical fast (few-10s seconds) ruptures to slow, long duration (100s of seconds) tsunami events, to s...

Seamounts are high relief features seen on many oceanic plates, including the Cocos plate offshore Costa Rica. As these features enter the subduction zone at Middle America Trench, they may perturb interface coupling by changing physical properties of the plate interface. Here we explore the role of seamounts on rupture process of microseismicity a...

Tsunami earthquakes are earthquakes that generate tsunami waves that are large with respect to their moment magnitude. The long rupture duration and low radiated energy (with respect to their moment magnitude) at long periods of these events imply that they are the result of the slow rupturing velocity and shallow rupture. Two examples, the 1994 an...

Seismicity in the Rio Grande rift in central New Mexico, southwestern United States, has been dominated by microearthquakes occurring above the midcrus-tal Socorro magma body (SMB) for at least the past century. The SMB is a sill-like feature ≥ 3400 km 2 in area, with a top surface at 19-km depth and centered below the inner rift half-graben system...

Nuclear test detection is a challenging, but important task for treaty verification. Many techniques have been developed to discriminate between an explosion and an earthquake and if an explosion is detected, to determine its yield. Sandia National Laboratories (SNL) has maintained the Leo Brady Seismic Network (LBSN) since 1960 to record nuclear t...

Subduction zones around the world release much of the world's seismic energy in mega- thrust earthquakes. This energy release varies in subduction zones around the world, likely related to heterogeneity in the strength of the mega-thrust zone. Here we examine the heterogeneity along the megathrust at the Middle America Trench, focusing on small mag...

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...

The majority of the world's largest earthquakes are confined to the subduction zone regions. Earthquake stress drop is an important parameter to characterize as it can illuminate changes in fault zone conditions. Here we determine stress drops for thrust zone earthquakes along the Nicoya Peninsula, Costa Rica to explore spatial variations in the Mi...

Offshore of the Nicoya Gulf at the Middle America Trench, the Cocos Plate is subducting beneath the Caribbean plate at about 84 mm per year. A line of seamounts are entering the trench in this region, causing dramatic deformation of the seafloor landward of the thrust. It has been suggested that these seamounts are being subducted, causing coastal...

The 26 December 2004 great Sumatran–Andaman earthquake in the Indian Ocean caused extensive damage and loss of life from intense shaking and the resulting tsunami. Several studies of this earthquake suggest that portions of the fault ruptured at variable speeds, with both fast and slow rupture velocities observed along the 1200 km long rupture leng...

Results from different tsunami forecasting and hazard assessment mod-els are compared with observed tsunami wave heights from the 26 December 2004 Indian Ocean tsunami. Forecast models are based on initial earthquake information and are used to estimate tsunami wave heights during propagation. An empirical forecast relationship based only on seismi...

Rupture models for large subduction zone earthquakes suggest significant heterogeneity in slip and moment release over the fault plane. Attempts to characterize the nature of the high-slip regions led to descriptions of these earthquakes in the context of the asperity model and allowed for subduction zones to be classified on the basis of likely ea...

The great Sumatra–Andaman earthquake of 26 December 2004 (UTC 00:58:53) was a momentous event, whether measured by scientific or human standards. Sadly, what is currently regarded as the third largest earthquake in recorded history led to the worst tsunami disaster in recorded history, with the loss of more than 200,000 lives and devastation throug...

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...

The July 17, 2006 M_W=7.7 earthquake ruptured south of western Java, Indonesia causing a locally devastating tsunami responsible for about 700 casualties. Early aftershocks in the shallow near-trench region which has had numerous small to moderate earthquakes in the past 30 years, similar to the 1994 slow-source "tsunami earthquake" (TsE) 500 km ea...

Seismicity in the Rio Grande Rift located in central New Mexico, southwestern U.S., is dominated by microearthquakes occurring above the mid-crustal Socorro Magma Body, a feature approximately 3000 km2 with a remarkably flat upper surface at 19 km depth. A recent swarm of microearthquakes began on October 20, 2005. The activity intensified toward O...

The shallow seismogenic zones of large subduction zone faults are of interest because the abundant seismicity (over 90% of global earthquakes) and the occurrence of the world's largest earthquakes, such as the Mw=9.2 Sumatra-Andaman earthquake of 2004. This shallow region is also host to other devastating earthquakes, such as the 2006 Java earthqua...

Source parameters affecting tsunami generation and propagation for the M w > 9.0 December 26, 2004 and the M w = 8.6 March 28, 2005 earthquakes are examined to explain the dramatic difference in tsunami observations. We evaluate both scalar measures (seismic moment, maximum slip, potential energy) and finite-source representations (distributed sl...

The March 1990 Mw=7.0 earthquake off the coast of Nicoya Peninsula, Costa Rica is thought to have been caused by the rupture of a seamount which acted as an asperity [Protti, 1995; Husen, et al., 2002]. An extensive local network recorded the event and the subsequent seismicity in the region, including aftershocks with magnitude greater than 1.5. T...

The two largest earthquakes of the past 40 years ruptured a 1600-kilometer-long portion of the fault boundary between the Indo-Australian and southeastern Eurasian plates on 26 December 2004 [seismic moment magnitude (M_w) = 9.1 to 9.3] and 28 March 2005 (M_w = 8.6). The first event generated a tsunami that caused more than 283,000 deaths. Fault sl...

The 26 December great Sumatran-Andaman earthquake in the Indian Ocean caused extensive damage and loss of life from intense shaking and the resulting tsunami. Recent studies of this earthquake have suggested portions of the fault ruptured at variable speeds, with both fast and slow rupture velocities observed along the 1200 km long rupture length [...

The devastating Indian Ocean tsunami of 2004 arose from complex source properties of the megathrust earthquake along the Sumatra-Andaman subduction zone. As we progress in our understanding of the only M>9 earthquake recorded by modern seismic and geodetic instruments, we look toward improving tsunami hazard assessment models. Standard models often...

Viscous flow in the mantle, by coupling to Earth's lithosphere, ultimately determines plate motions, lithospheric stresses, and patterns of seismicity. To constrain the mantle's influence on these varied observables, we synthesize recent predictions of plate motions and lithospheric stresses determined from self-consistent models of mantle flow. We...

1] Subduction zone seismicity is highly variable. Great earthquakes occur at few subduction zones around the world, with significant variation in size and frequency of deep events. Interactions between overriding and subducting plates and slab pull strength for individual plates provide a framework for understanding these variations. Previous work...

The two largest earthquakes of the past 40 years ruptured a 1600-kilometer-long portion of the fault boundary between the Indo-Australian and southeastern Eurasian plates on 26 December 2004 [seismic moment magnitude (Mw) = 9.1 to 9.3] and 28 March 2005 (Mw = 8.6). The first event generated a tsunami that caused more than 283,000 deaths. Fault slip...

Two recent earthquakes near the west coast of Sumatra are the largest to occur in any subduction zone since the 1960s. The December 2004 MW=9.0 Andaman-Sumatra earthquake caused extensive damage and loss of life from both strong shaking and massive transoceanic tsunami. This event began near Bande Aceh and ruptured northward along the trench nearly...

Stress changes after large earthquakes can trigger substantial seismicity along many fault systems. As subduction zones produce the majority of large earthquakes, it is essential to understand how significant earthquakes may affect stress conditions and aftershock locations. Calculations of stress changes due to large underthrusting earthquakes can...

Subduction zone seismicity occurs at some of the largest population centers in the world, increasing the need for greater understanding of the processes that occur in these areas. Among the complexities of the physical relationships involved in subduction zone processes is the role of subducting plate topography in slip and rupture. Subduction zone...

Previous studies of global subduction zone earthquake rupture processes have found examples of shallow earthquakes that exhibit depth dependent durations, with the longest durations observed for the several of the shallowest earthquakes. The long durations, after scaled for earthquake size, are comparable to those durations found for tsunami earthq...

Earthquake source time functions deconvolved from teleseismic broadband P wave recordings are used to examine rupture variations for 417 underthrusting earthquakes located on the interplate interface in circum-Pacific subduction zones. Moment-scaled duration of significant moment release varies with depth, with longer-duration events occurring in t...

Previous studies used seismic energy to moment ratios for datasets of large earthquakes as a useful discriminant for tsunami earthquakes. We extend this idea of a "slowness" discriminant to a large dataset of subduction zone underthrusting earthquakes. We determined estimates of energy release in these shallow earthquakes using a large dataset of s...

Great earthquakes, the few largest earthquakes that account for most of the Earth’s seismic energy release, have occurred at only a few subduction zones around the world. Strong locking, or ‘seismic coupling’, of the interface between plates at certain subduction zones is often invoked to explain these great earthquakes. Although past studies have...

There are several cases of interaction between subducting bathymetric features and large subduction zone earthquakes. For large earthquakes in the Nankai subduction zone, it appears that subducted features have acted as barriers to rupture along the plate boundary. In other regions, such as Costa Rica and Java, subducted seamounts appear to be in r...

1] The shallow seismogenic portion of subduction zones generates damaging large and great earthquakes. This study provides structural constraints on the seismogenic zone of the Middle America Trench offshore central Costa Rica and insights into the physical and mechanical characteristics controlling seismogenesis. We have located $300 events that o...