John E Vidale

• PhD
• Professor (Full) at University of Washington

The inner core has been inferred to change its rotation rate or shape over years to decades since the discovery of temporal variability in seismic waves from repeating earthquakes that travelled through the inner core. Recent work confirmed that the inner core rotated faster and then slower than the rest of Earth in the last few decades; this work...

The core‐mantle boundary (CMB) and the outermost core are dynamic and heterogeneous regions with time‐dependent flows. We examine two seismic raypaths, diffracted P and PKP precursors—both replete with scattering, with precisely repeating earthquakes. These earthquakes, occurring in the South Sandwich Islands, were recorded on the Yellowknife array...

Sedimentary basins in the Puget Sound region, Washington State, increase ground-motion intensity and duration of shaking during local earthquakes. We analyze Pacific Northwest Seismic Network and U.S. Geological Survey strong-motion recordings of five local earthquakes (M 3.9–6.8), including the 2001 Nisqually earthquake, to characterize sedimentar...

Deep sedimentary basins amplify long‐period shaking from seismic waves, increasing the seismic hazard for cities sited on such basins. We perform 3‐D simulations of point source earthquakes distributed around the Seattle and Tacoma basins in Washington State to examine the dependence of basin amplification on source azimuth, depth, and earthquake t...

We used a combination of 3D finite-difference simulations (< 1 Hz) and 1D stochastic synthetics (> 1 Hz) to generate broadband (0-10 Hz) synthetic seismograms for numerous M w 9 earthquake rupture scenarios on the Cascadia megathrust. Slip consists of multiple high-stress-drop subevents (M w 8) with short rise times on the deeper portions of the fa...

The Cascadia Subduction Zone (CSZ) produces long-duration, large-magnitude earthquakes that could severely affect structures in the Pacific Northwest (PNW). The impact of synthetic M9.0 CSZ earthquakes on buildings in the Pacific Northwest is studied using eight reinforced concrete wall archetypes that range from 4 to 40 stories. These archetypes w...

Volcanic deep long-period earthquakes (DLPs) have been observed for a long time but remain poorly understood. In this study, 22 catalog DLPs were taken as templates to search for repeating events at Mount St. Helens. During the period from 2007 to 2016, we have detected 277 DLPs. Three templates are isolated DLPs, while all other templates produced...

The importance of Global Navigation Satellite System (GNSS)-based earthquake early warning for modeling large earthquakes has been studied extensively over the past decade, and several such systems are currently under development. In the Pacific Northwest, we developed the Geodetic First Approximation of Size and Timing (G-FAST) GNSS-based earthqua...

We present a catalog of offshore seismicity generated from Cascadia Initiative (CI) ocean-bottom seismometer data. Earthquakes were detected within the CI data using a short-time-average/long-time-average trigger and located using 1D velocity models developed from seismic reflection/refraction surveys. The catalog, which contains 271 earthquakes wi...

We compare broadband synthetic seismograms with recordings of the 2003 Mw 8.3 Tokachi-Oki earthquake to evaluate a compound rupture model, in which slip on the fault consists of multiple high-stress-drop asperities superimposed on a background slip distribution with longer rise times. Low-frequency synthetics (<1 Hz) are calculated using determinis...

The motivation for earthquake early warning (EEW) is the fact that in many applications a few extra seconds of notice ahead of the about-imminent strong shaking can provide significant benefit. Reducing data latencies, accelerating processing times, and tuning seismic station distributions increase time available for warning. We assess the feasibil...

Every few hundred years, the Cascadia subduction zone off the coast of the Pacific Northwest hosts devastating earthquakes, and there is a growing awareness of the need to be prepared for these events. An offshore cabled observatory extending the length of the Cascadia subduction zone would enhance the performance of the earthquake and tsunami earl...

We evaluate the performance of earthquake early warning algorithm ElarmS-2 (earthquake alarm system v. 2) in the Pacific Northwest. Real-time and prerecorded seismic data from Oregon, California, and Washington in the United States and British Columbia in Canada are used. The earthquakes tested range up to moment magnitude 7.2, the limit for which...

A prototype earthquake early warning (EEW) system is currently in development in the Pacific Northwest. We have taken a two-stage approach to EEW: (1) detection and initial characterization using strong-motion data with the Earthquake Alarm Systems (ElarmS) seismic early warning package and (2) the triggering of geodetic modeling modules using Glob...

Mount St. Helens began erupting in late 2004 following an 18year quiescence. Swarms of repeating earthquakes accompanied the extrusion of a mostly solid dacite dome over the next 4years. In some cases the waveforms from these earthquakes evolved slowly, likely reflecting changes in the properties of the volcano that affect seismic wave propagation....

The correlation of earthquakes with tremor and slow slip has not been clearly quantified. We investigate 12-year earthquake and tremor catalogs for Southwest Japan, and find that nearby small intraslab earthquakes are weakly correlated with tremor. In particular, the intraslab earthquakes with magnitudes ≥2.7 tend to be followed by tremor more ofte...

[1] In September 2004, Mount St. Helens (MSH) volcano erupted after nearly 18 years of quiescence. However, it is unclear from the limited geophysical observations when or if the magma chamber replenished following the 1980-1986 eruptions, in the years before the 2004-2008 extrusive eruption. We use coda-wave interferometry with repeating earthquak...

[1] Here we report on deep long-period earthquakes (DLPs) newly observed in four places in western Oregon. The DLPs are noteworthy for their location within the subduction forearc: 40 – 80 km west of the volcanic arc, well above the slab, and near the Moho. These “offset DLPs” occur near the top of the inferred stagnant mantle wedge, which is likel...

We demonstrate the value of utilizing broadband synthetic seismograms to assess regional seismically induced landslide hazard. Focusing on a case study of an M-w 7.0 Seattle fault earthquake in Seattle, Washington, we computed broadband synthetic seismograms that account for rupture directivity and 3D basin amplification. We then adjusted the compu...

[1] We provide a new link between tectonic tremor propagation, tremor amplitude, and tidal stresses by analyzing high-resolution tremor locations and amplitudes determined by multibeam backprojection of data from an array of subarrays. For two Cascadia episodic tremor and slip events, we observe repeating, high-amplitude rapid tremor reversals (RTR...

During the 2009 eruption of Redoubt Volcano, Alaska, gliding harmonic tremor occurred prominently before six nearly consecutive explosions during the second half of the eruptive sequence. The fundamental frequency re-peatedly glided upward from b 1 Hz to as high as 30 Hz in less than 10 min, followed by a relative seismic quies-cence of 10 to 60 s...

Mount St. Helens is one of the most societally relevant and geologically interesting volcanoes in the United States. Although much has been learned about the shallow structure of this volcano since its eruption in 1980, important questions still remain regarding its magmatic system and connectivity to the rest of the Cascadia arc. For example, the...

Slow earthquakes, characterized by slow slip and associated seismic radiation called non-volcanic tremor, have been observed in major subduction zones worldwide. They constitute an important mode of stress release for the fault's transition zone, which lies directly downdip of the locked segment, the nucleation zone of large damaging earthquakes. H...

The Natural Resources Building (NRB) in Olympia, Washington, was shaken by three earthquakes (Mw = 5.8, 6.8, and 5.0) between 1999 and 2001. Building motions were recorded on digital accelerographs, providing important digital recordings of repeated strong shaking in a building. The NRB has 5-stories above grade with 3 sub-grade levels and a ductil...

Models of seismic source displacement spectra are flat from zero to some corner frequency, fc, regardless of source type. At higher frequencies spectral models decay as f-1 for slow events and as f-2 for fast earthquakes. We show that at least in Cascadia, wave propagation effects likely control spectral decay rates above ˜2 Hz. We use seismograms...

Sandwiched between the shallow region of sudden, infrequent earthquakes and the deeper home to continuous viscous motion lies an intermediate realm of intermittent sliding and rumbling. Discovered in recent years, it still harbors many secrets.

Slow earthquakes, characterized by slow slip and associated seismic radiation called non-volcanic tremor, have been observed in major subduction zones worldwide. They are an important mode of stress release for the fault's transition zone, which lies directly down-dip of the locked segment, the nucleation zone of large damaging earthquakes. However...

We captured the major August 2010 slow slip episode near the Puget Sound in Cascadia with an unprecedented density of seismometers. The EarthScope Array of Arrays had eight 1-km-aperture, 20+ station arrays, and we also had numerous individual stations in the CAFÉ experiment and the permanent regional PNSN network. With a range of methods, we are i...

It is generally accepted that spectral characteristics distinguish 'slow' seismic sources from those of 'ordinary' or 'fast' earthquakes. To explore this difference, we measure ordinary earthquake spectra of about 30 seismic events located near the Cascadia plate interface where ETS regularly occurs. We separate the affects of local site response,...

NetQuakes accelerographs are relatively inexpensive Internet-aware appliances that we are using as part of our regional seismic monitoring program in the Pacific Northwest Seismic Network (PNSN). To date we have deployed approximately 65 units. By the end of 2011, we will have at least 75 systems sited and operating. The instruments are made by Swi...

The fascinating propagation behavior of the rupture front during episodic tremor and slip (ETS) events in Cascadia and Japan has received a great deal of attention documenting a roughly 8 km/day along-strike propagation, rapid tremor reversals propagating an order of magnitude faster, and tremor streaks aligned with the slip vector propagating two...

It has been proposed that shallow, frequently-repeating long-period earthquakes (LPs) are the underlying source of volcanic tremor. We demonstrate for several andesitic and dacitic volcanoes that repeating earthquakes and tremor do share a common source. This hypothesis is based on similar spectral content and the observations of earthquakes mergin...

Seismically induced landsliding has caused extensive loss of life and damage in many historical earthquakes, but has not been comprehensively assessed for Seattle, a city prone to both landslides and earthquakes. To remedy this, we take advantage of the wealth of detailed static slope stability and geological data now available. With them, we use a...

The discovery of non-volcanic tremor (NVT) has opened a new window to observe major Earth plate boundaries. However, the spectral characteristics of NVT have not been well studied due to poor signal-to-noise ratio (SNR) on individual seismograms. We estimate the spectral content of Cascadia tremor between 2.5 and 20 Hz by suppressing noise using ar...

Tomography with short-period Rayleigh waves, extracted using noise interferometry, can refine S-wave velocity (V-S) models in urban areas with dense arrays of short-period and broadband instruments. We apply this technique to the Seattle area to develop a new shallow V-S model for use in seismic-hazard assessment. Continuous data from the Seismic H...

Episodic tremor and slip (ETS) has been observed in many subduction zones, but its mechanical underpinnings as well as its potential for triggering damaging earthquakes have proven difficult to assess. Here we use a seismic array in Cascadia of unprecedented density to monitor seismicity around a moderate 16 day ETS episode. In the 4 months of data...

Deep long-period (DLP) earthquakes are an enigmatic type of seismicity occurring near or beneath volcanoes. They are commonly associated with the presence of magma, and found in some cases to correlate with eruptive activity. To more thoroughly understand and characterize DLP occurrence near volcanoes in Washington and Oregon, we systematically sea...

Non-volcanic tremor is notoriously difficult to locate due to its emergent nature and lack of distinct phases. Although a variety of techniques have been used to locate tremor in Cascadia, depth resolution remains problematic and tremor locations are often scattered in depth. Some researchers have argued that this wide depth distribution is real an...

The spectral decay of non-volcanic tremor (NVT) contains important information about the physical processes involved in Episodic Tremor and Slip (ETS). Using a small-aperture seismic array deployed on Big Skidder Hill, WA, we employ frequency-domain beamforming to obtain spatiotemporal spectral estimates of NVT activity in Cascadia on May 6-19, 200...

Occasionally volcanic tremor's dominant frequency and its overtones change continuously with time, or `glide'. Gliding spectral lines have been described on volcanoes of varying sizes and compositions. During the most recent eruption of Redoubt Volcano, Alaska, gliding spectral lines appear prominently before five nearly consecutive explosions of t...

Low-frequency earthquakes (LFEs) are a recently identified class of earthquakes that have been observed to occur coincidentally with tectonic tremor in time and space. These LFEs also have a frequency spectra that is nearly identical to that of tectonic tremor---implying a common source for these two phenomena. As demonstrated by Shelly et al. (200...

Nonvolcanic tremor is a recently discovered weak seismic signal associated with slow slip on a fault plane and has potential to answer many questions about how faults move. Its spatiotemporal distribution, however, is complex and varies over different time scales, and the causal physical mechanisms remain unclear. Here we use a beam backprojection...

Episodic tremor and slip (ETS) events, each with geodetically determined moment magnitudes in the mid-6 range, repeat about every 15 months under the Olympic Peninsula/southern Vancouver Island region. We have applied an automatic waveform envelope cross-correlation and clustering (WECC) algorithm to seven Cascadia-wide subarrays to search for non-...

We are capturing the intimate details of tremor activity in Cascadia with 8 small-aperture seismic arrays in northwestern Washington. The Array of Arrays (AoA) focuses on the tremor-active megathrust, including the area we previously imaged with a solo seismic array in 2008 [Ghosh et al., GRL, 2009, 2010]. Each array consists of 10 to 20 three-comp...

Aiming to peek at the inner life of tremor activity, we planted eight small-aperture seismic arrays with about 100 seismometers in northern Washington in summer 2009, augmented by 80 more during the major tremor episode. The AoA surrounds a particularly tremor-active region of the Cascadia megathrust, including the area that we previously imaged wi...

Much of Seattle lies atop a deep sedimentary basin. The Seattle Basin amplifies and distorts seismic waves in ways that modulate the hazard from earthquakes. Seismic hazard assessments heavily depend upon upper crustal and near-surface S-wave velocity models. Improving the accuracy and resolution of basin S-wave models is key to improving predictio...

We observed a swarm of repeating sequences of seismic events during three weeks in May and June 2010 near the summit of Mount Rainier, Washington. These sequences likely marked stick-slip motion at the base of alpine glaciers. The dominant set of nearly identical earthquakes repeated more than 4000 times and had no diurnal variation in recurrence i...

Major episodic tremor and slip (ETS) events with Mw 6.4 to 6.7 repeat every 15 ± 2 months within the Cascadia subduction zone under the Olympic Peninsula. Although these major ETS events are observed to release strain, smaller ``tremor swarms'' without detectable geodetic deformation are more frequent. An automatic search from 2006-2009 reveals 20,...

Much of Seattle, in the northwestern United States, lies atop a sedimentary basin that extends approximately 9 km deep. The basin structure is the result of the evolution of the Puget Lowland fore arc, which combines strike-slip and thrust-fault movements to accommodate right-lateral strike-slip and N-S shortening due to the oblique subduction of t...

During the slow slip events in Cascadia and Japan, a well-documented feature of nonvolcanic tremor (NVT) is its puzzling slow along-strike migration. But the cause, possible implications, and underlying physics of this long-term tremor migration and its relationship with slow slip remain elusive. Here, we use tremor data recorded by a dense seismic...

In several instances, the passing surface waves from large earthquakes have ignited nonvolcanic tremor (NVT) on major faults. Still, the mechanism of tremor and its reaction to the dynamic stressing from various body and surface waves is poorly understood. We examine tremor near Parkfield, California, beneath the San Andreas fault triggered by the...

The known universe of tectonic fault behavior has gained a new neighborhood in the last few years. Before, faults were considered to either conform to the reasonably well-understood earthquake cycle or else slide steadily. In the earthquake cycle, a fault stays locked for the years while stress is accumulating, then cracks and slides, releasing abo...

Episodic tremor and slip (ETS) has been observed along the Cascadia subduction zone at a depth range of 30-45 km. There is strong evidence that the tremor occurring at this location is modulated by tidal stresses. More than 16,000 automatically detected and located tremor epicenters from January 2007 through June 2009 have been correlated with a ti...

We examined rock damage and healing on the Longmen-Shan Fault (LSF) that ruptured in the 2008 M8 Wenchuan earthquake using the data recorded at Sichuan Seismic Network and portable stations. The Wenchuan mainshock included multiple events with the reverse thrusting at the first stage and then becoming to strike-slip gradually, indicating the comple...

The Pacific Northwest Seismic Network (PNSN) records and locates earthquakes within Washington and Oregon, including those occurring at 10 Cascade volcanic centers. In an earlier study (Malone and Moran, EOS 1997), a total of 11 deep long-period (DLP) earthquakes were reported beneath 3 Washington volcanoes. They are characterized by emergent P- an...

Recent observations of non-volcanic tremor in Cascadia and Japan show ``streaks'' of tremor moving up and down dip in a convergence-parallel direction at ``driving velocities'' (i.e., 30 to 120 km/hr). Streak lengths of 30 to 40 km are occasionally observed. We explore the implications of these observations for a source model and spectrum of tremor...

Low-frequency earthquakes (LFEs) are a recently identified class of earthquakes that have been observed to occur coincidentally with non-volcanic tremor in time and space. These LFEs also have a frequency spectra that is nearly identical to that of tremor—implying a common source for these two phenomena. Indeed, it has been proposed that tremor may...

Episodic tremor and slip (ETS) events, each with geodetically determined moment magnitudes in the mid-6 range, repeat about every 15 months under the Olympic Peninsula/southern Vancouver Island region. We have automatically searched for non-volcanic tremor in all 5-minute time windows both during the past five ETS events and during the two inter-ET...

Episodic tremor and slip (ETS) events in Cascadia have recently been observed, illuminating the general area that radiates seismic energy in the form of non-volcanic tremor (NVT). However, the picture of the ETS zone remains fuzzy because of difficulties in tremor detection and location. To observe the intimate details of tremor, we deployed a dens...

We perform a systematic survey of triggered tremor along the San Andreas Fault in central California for the 31 teleseismic earthquakes with Mw ≥ 7.5 since 2001. We identify 10 teleseismic events associated with clear triggered tremor. About 52% of the tremor is concentrated south of Parkfield near Cholame, where ambient tremor has been identified...

Episodic tremor and slip (ETS) events, each with geodetically determined moment magnitudes in the mid-6 range, repeat with remarkable regularity every 15 months under the Olympic Peninsula/southern Vancouver Island region. We have automatically searched for non-volcanic tremor in all 5-minute time windows both during the past 4 ETS events and durin...

During earthquakes, slip is often localized on preexisting faults, but it is not well understood how the structure of crustal faults may contribute to slip localization and energetics. Growing evidence sug- gests that the crust along active faults undergoes anomalous strain and damage during large earthquakes. Seismic and geodetic data from the Cal...

1] We explore the physical conditions that enable triggering of nonvolcanic tremor and earthquakes by considering local seismic activity on Vancouver Island, British Columbia during and immediately after the arrival of large-amplitude seismic waves from 30 teleseismic and 17 regional or local earthquakes. We identify tremor triggered by four of the...

Nonvolcanic tremor is difficult to locate because it does not produce impulsive phases identifiable across a seismic network. An alternative approach to identifying specific phases is to measure the lag between the S and P waves. We cross-correlate vertical and horizontal seismograms to reveal signals common to both, but with the horizontal delayed...

Details of tremor deep in subduction zones is damnably difficult to glimpse because of the lack of crisp initial arrivals, low waveform coherence, uncertain focal mechanisms, and the probability of simultaneous activity across extended regions. Yet such details hold out the best hope to illuminate the unknown mechanisms underlying episodic tremor a...

We show clear evidence of non-volcanic tremor triggered by 2002 Mw7.8 Denali Fault earthquake near Parkfield. Triggered tremor is identified as bursts of high-frequency (~2-8 Hz), non-impulsive seismic energy whose envelope is coherent among many stations and has the same periodicity as the passing surface waves. The tremor originates from at least...

Low-frequency earthquakes (LFEs) were first reported in Japan and have been observed to occur coincidently with non-volcanic tremor in both space and time. Compared to similarly-sized ordinary earthquakes, LFEs are deficient in frequencies above 5 Hz. The frequency spectrum of LFEs mirrors the spectrum of tremor. Indeed Shelly et al. (2006, 2007, N...

We have automatically searched Northwestern Washington for non-volcanic tremor in all 5-minute time windows during the inter-ETS period from February, 2007 through April, 2008. Tremor was detected in nearly 3000 windows, which overlap by 50%, so tremor was seen 2% of the time. The catalog of 5-minute tremor locations cluster in time and space into...

Aspiring to see more intimate details, we placed an 84-element short-period vertical-component array with an aperture of 1km on a hard rock mountain over the path of Cascadia tremor. This site is coincident with a stellar 6-station three-component CAFE array (see talk by K. Creager). Texans, which are convenient to deploy but require recycling for...

We perform a systematic survey of triggered tremor around the Parkfield section of the San Andreas fault for the 31 teleseismic earthquakes since 2001 with Mw >= 7.5 and depth < 100 km. We identify triggered tremor as bursts of high-frequency (~2-8 Hz), non-impulsive seismic energy that are generated during the passage of teleseismic waves and cohe...

Episodic Tremor and Slip (AKA ETS) is appearing numerous unsuspected places as seismic instruments and analysis gears up into the 21st century. From its initial and loudest lair in subduction zones, ETS observations have spread to strike-slip faults and fold-thrust belts. ETS differs from old-school earthquakes. ETS can last weeks while the grandes...

Earthquakes cluster strongly in time and space, but it is not yet clear how much of this clustering can be explained as triggering from previous events (such as occurs for aftershock sequences following large earthquakes) and how much the clustering may reflect underlying physical processes (such as slow slip or fluid flow). Here we examine recent...

In several instances, the passing surface waves from large earthquakes have ignited non-volcanic tremor (NVT) on major faults. Still, the mechanism of tremor and its reaction to the dynamic stressing from different body and surface waves is poorly understood. We examine tremor around Parkfield, California near the San Andreas Fault triggered by the...

We report preliminary analyses from a 5-station portable broadband seismic array deployed around a site of persistent swarm-like earthquakes near the town of Maupin in north central Oregon. Swarm behavior is common amongst crustal earthquakes in Cascadia, particularly east of the Cascades where seismic instrumentation is sparse and seismicity may b...

Seismic hazard assessments depend heavily on near-surface S-wave velocity models. Here we present a basin-wide 3-D shear wave velocity model based on direct observations, rather than inferred from P-wave velocities. Shallow S-wave velocities are determined by near-surface geology, which in the Seattle area is a combination of crystalline rock, glac...

We have placed instruments in the UW (formerly SafeCo) Tower and on the Alaska Way Viaduct in Seattle to monitor their motions. Monitoring conventionally provides information on site response and real time measurements of shaking during earthquakes. We are also investigating the possibility of monitoring the fundamental modes of the structures as a...

The Natural Resources Building (NRB) in Olympia was shaken by three earthquakes (Mw=5.8, 6.8, and 5.0) between 1999 and 2001. Building motions were recorded on digital accelerographs, which comprise one of the best dense digital recordings to date of repeated strong shaking an a building. N-S motions dominate the fundamental mode of vibration of th...

A growing number of observations show that seismic waves trigger tremor. These observations are providing key constraints on mechanisms of tremor generation. Triggered tremor refers to bursts of seismic energy with the same characteristics as ambient tremor but are temporally modulated by the triggering seismic waves. We hypothesize that triggered...

Hi Luciana, I read with interest the July–August 2008 article in SRL “Seismic Raves: Tremor observations from an electronic music festival,” by David N. Green and David Bowers. The authors describe harmonic signals recorded coincident with the 2007 Glade Festival and make an excellent case that the festival generated the 2–3 Hz signals. However,...

[1] Recent observations of inner-core scattering (ICS) waves provide evidence that the outermost 300 km of the inner-core has strong heterogeneities with a length scale of a few kilometers. These waves follow a path similar to that of the inner-core–reflected waves PKiKP and were originally observed in data from 16 events in the distance range 58 t...

We observe that broadband seismometers may produce artifact long-period signals that resemble impulse responses, similar to a step in acceleration, in the presence of shaking as moderate as 0.2% g. This observation accords with recent observations in Europe and elsewhere with similar instruments ( e. g., Zahradnik and Plesinger, 2005). We present t...

Episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of Japan and Cascadia. In Cascadia, such episodes typically last a few weeks and differ from "normal" earthquakes in their source location and moment-duration scaling. The three most recent episodes in the Puget Sound/southern Vancouver Isl...

We identified seven locations on or near the transform plate boundary in California where nonvolcanic tremor was triggered by the 2002 Denali earthquake. This result implies that the conditions essential for nonvolcanic tremor exist in a range of tectonic environments. Models explaining tremor typically require conditions endemic to subduction zone...

The tremor triggered near Parkfield, CA by the 2002 Denali and 2004 Sumatra earthquakes was strong and well recorded by the dense regional CISN and the borehole HRSN networks. Peng et al. (this meeting) survey tremors triggered by a larger set of 12 regional and teleseismic events, providing a broader context. In the case of both the 2002 M7.9 Dena...

Emergent, low-slowness coda waves following precritical PKiKP phases have now been observed at a geographically and geometrically diverse set of seismic arrays. Forward simulations using ray-theoretical single scattering theories have shown that it is difficult to match the observed properties with heterogeneity in the mantle, along the core-mantle...

We summarize efforts to tailor ShakeMap to the Pacific Northwest Seismic Network (PNSN), and to increase the resolution in the major urban areas. Our initial implementation of ShakeMap employed parameters based on data from mostly larger earthquakes outside the Pacific Northwest. The PNSN automatically generates a 45- arcsec ShakeMap for any earthq...

Seismic hazard assessments depend heavily on near-surface S-wave velocity models. Local S-wave velocity models have traditionally been constructed from P-wave models using a deterministic relationship between P- wave and S-wave velocity, or by interpolating within widely spaced observations of geologic structure. Direct measurement of local S-wave...

We identify bursts of tremor that radiated from the Cascadia subduction zone near Vancouver Island, Canada, during the strongest shaking from the moment magnitude Mw = 7.8, 2002 Denali, Alaska earthquake. Tremor occurs when the Love wave displacements are to the southwest (the direction of plate convergence of the overriding plate) strongly suggest...

The recent discovery of non-volcanic tremor has led to great excitement and research activity in the earth-science community. To date, tremor has almost exclusively been found in subduction zones. The only observation outside a subduction-dominated region is on the strike-slip San Andreas Fault in Parkfield, California. In Japan and Cascadia non-vo...

The July 2004, September 2005 and January 2007 episodic tremor and slip events in the Puget Sound/Vancouver Island ETS source region, were exceptionally well recorded by temporary deployments of small-aperture seismic arrays. Analysis of stacked, filtered envelope functions across these arrays shows a clear pulsing of tremor activity with strong, i...

After the M6 Parkfield earthquake that occurred on 28 September 2004, we deployed a dense seismic array at the same sites as used in our experiment in the fall of 2002. The measurements using moving-window cross- correlation of waveforms for the repeated explosions and microearthquakes recorded in 2002 and 2004 show a decrease in shear velocity of...

Non-volcanic tremor triggered by teleseismic waves was discovered recently along the subduction zones in Japan and Cascadia, and along the transform plate boundary in CA. Here we summarize non-volcanic tremor along the San Andreas fault (SAF) near Parkfield, CA triggered by the surface waves of regional and teleseismic events. We analyze 10 M ≥ 8.0...

Highly damaged rocks along the San Andreas Fault at Parkfield create a low-velocity waveguide to trap seismic waves. We recorded prominent fault-zone trapped waves (FZTWs) at the SAFOD mainhole seismograph at 3km depth and the surface seismic array across the fault for microearthquakes. A systematic waveform analysis of borehole and surface seismog...

Seismograms from a dense, high-quality seismic network in Japan are used to investigate the characteristics of the 26 December 2004 Sumatra-Andaman and the 28 March 2005 Sumatran earthquakes. The onset of the P waveforms are aligned through cross correlation, and a simple concept of back-projecting seismic energy to a grid of potential source locat...