Valerie J. Sahakian

• Ph.D. Earth Science
• Professor (Assistant) at University of Oregon

Tsunami earthquakes produce some of the most devastating tsunamis. These rare events have comparatively modest magnitudes but rupture the shallowest portion of a subduction zone megathrust with exceptionally large seafloor displacements. Previous teleseismic observations found that they radiate seismic waves weakly. They should therefore not be str...

Traditional, empirical ground-motion models (GMMs) are developed by prescribing a functional form between predictive parameters and ground-motion intensity measures. Machine-learning techniques may serve as a fully data-driven alternative to widely used regression techniques, as they do not require explicitly defining these relationships. Although,...

Ground‐motion studies are a key component of seismic hazard analyses and often rely on information of the source, path, and site. Extensive research has been done on each of these parameters; however, site‐specific studies are of particular interest to seismic hazard studies, especially in the field of earthquake engineering, as near‐site condition...

To provide timely and accurate seismic alerts for potential users during the earthquake early warning process, several algorithms have been proposed and implemented. Some of the most common rely on the characterization of the earthquake magnitude and location, and then use a ground motion model to forecast shaking intensity at a user's location. It...

Subduction zone earthquakes result in some of the most devastating natural hazards on Earth. Knowledge of where great (moment magnitude M ≥ 8) subduction zone earthquakes can occur and how they rupture is critical to constraining future seismic and tsunami hazards. Since the occurrence of well-instrumented great earthquakes, such as the 2004 M9.1 S...

We use a combination of near-field simulated and observational data to constrain the rise time, rupture velocity, and high frequency stress parameter for the 2010 M7.8 Mentawai tsunami earthquake. Tsunami earthquakes, which are shallow-rupturing events generating exceptionally large seafloor displacements, are challenging for current tsunami early...

Accurately modeling time-dependent coseismic crustal deformation as observed on high-rate Global Navigation Satellite System (HR-GNSS) lends insight into earthquake source processes and improves local earthquake and tsunami early warning algorithms. Currently, time-dependent crustal deformation modeling relies most frequently on simplified 1D radia...

Scientists are making progress on illuminating how undersea sedimentary deposits called turbidites form and on reconstructing the complex histories they record. But it’s not an easy task.

Earthquake early warning (EEW) systems aim to forecast the shaking intensity rapidly after an earthquake occurs and send warnings to affected areas before the onset of strong shaking. The system relies on rapid and accurate estimation of earthquake source parameters. However, it is known that source estimation for large ruptures in real‐time is cha...

Accurately modeling time-dependent coseismic crustal deformation as observed on high-rate Global Navigation Satellite System (HR-GNSS) lends insight into earthquake source processes and improves local earthquake and tsunami early warning algorithms. Currently, time-dependent crustal deformation modeling relies most frequently on simplified 1D radia...

Figures 3 and 4 were switched in the published paper. Below shows the correct figures and their captions.

We investigate the effects of site response on source parameters using earthquakes recorded by a dense nodal array in Oklahoma. While it is well-known that near-surface unconsolidated sediments can cause an apparent breakdown of earthquake self-similarity, the influence of laterally varying site conditions remains unclear. We analyze site condition...

Site characterization is a critical component of seismic hazards studies, especially in the development and use of ground motion models (GMMs). One such parameter, kappa (k0), represents local site attenuation and effectively describes regional variations in ground motion [1]. However, estimates of k0 are limited. We estimate the site parameter k0...

In the tectonically complex Imperial Valley, California (USA), the Imperial fault (IF) is often considered to be the primary fault at the U.S.-Mexico border; however, its strain partitioning and interactions with other faults are not well understood. Despite inferred evidence of other major faults (e.g., seismicity), it is difficult to obtain a hol...

Plain Language Summary We know that large earthquakes at the Cascadia subduction zone, in the Pacific Northwest of the U.S., are possible. In order to understand how strong shaking will be when this occurs and how the coast will subside, we need to know how deep into the Earth the fault can move. The deeper this limit is, the stronger the shaking w...

In this presentation, we discuss our methodology for estimating the site parameter, k0, for 296 broadband and accelerometer stations in the San Francisco Bay area. We deviate from our initial methods outlined in the SSA 2021 conference presentation and instead use the k_AS (acceleration spectrum) method (Anderson and Hough, 1984; Anderson 1991; Kte...

At subduction zones, the down-dip limit of slip represents how deep an earthquake can rupture. For hazards it is important - it controls the intensity of shaking and the pattern of coseismic uplift and subsidence. In the Cascadia Subduction Zone, because no large magnitude events have been observed in instrumental times, the limit is inferred from...

We present an updated ground-motion model (GMM) for Mw 6–9 earthquakes using Global Navigation Satellite Systems (GNSS) observations of the peak ground displacement (PGD). Earthquake GMMs inform a range of Earth science and engineering applications, including source characterization, seismic hazard evaluations, loss estimates, and seismic design st...

The Cascadia subduction zone (CSZ) is an exceptional geologic environment for recording evidence of land-level changes, tsunamis, and ground motion that reveals at least 19 great megathrust earthquakes over the past 10 kyr. Such earthquakes are among the most impactful natural hazards on Earth, transcend national boundaries, and can have global imp...

In this presentation, we discuss our methodology for estimating the site parameter, k0, for 30 broadband stations in the San Francisco Bay area. We follow the spectral decomposition approach outlined in Klimasewski et al. (2019). Preliminary results show k0 to vary strongly, but overall estimates are moderate. We have since adjusted our methodology...

In this poster presentation, we outline the methodology for generating synthetic data using a set of semistochastic forward-modeling codes, referred to as FakeQuakes. We vary the rupture parameters stress drop, rise time, and rupture velocity to try to constrain the values for a tsunami earthquake scenario. Preliminary results show that varying sou...

The U.S. Pacific Northwest (PNW) is one of the largest Internet infrastructure hubs for several cloud and content providers, research networks, colocation facilities, and submarine cable deployments. Yet, this region is within the Cascadia Subduction Zone and currently lacks a quantitative understanding of the resilience of the Internet infrastruct...

Location, Location, Location: Turbidite stratigraphy at the interface between paleoseismic and paleoclimate records C. Goldfinger. M. Walczak, V. Sahakian, Brendan Reilly, Saray Valdez Hernandez Paleoseismic turbidites along the Cascadia margin are spatially restricted, more so than one might expect. Excellent high-resolution records are found in...

Plain Language Summary The San Andreas is a right‐lateral strike‐slip fault marking the main tectonic boundary between the North American and Pacific Plates. East of the San Andreas, a diffuse region of right‐lateral shear known as the Eastern California Shear Zone accommodates roughly one quarter of the motion between the two tectonic plates. The...

The July 4, 2019 Mw6.4 and subsequent July 6, 2019 Mw7.1 Ridgecrest Sequence earthquakes ruptured orthogonal fault planes in the Little Lake Fault Zone, a low slip rate (1 mm/yr) dextral fault zone in the area linking the Eastern California Shear Zone and Walker Lane. This region accommodates nearly one fourth of plate boundary motion and has been...

Ground‐motion modeling requires accurate representation of the earthquake source, path, and site. Site amplification is often modeled by VS30, the time‐averaged shear‐wave velocity of the top 30 m of the Earth’s surface, though recent studies find that its ability to accurately predict site effects varies. Another measure of the site is κ0, the att...

To improve models of ground motion estimation and probabilistic seismic hazard analyses, the engineering seismology field is moving toward developing fully nonergodic ground motion models, models specific for individual source‐to‐site paths. Previous work on this topic has examined systematic variations in ground‐motion along particular paths (from...

The 2017 M 8.2 Tehuantepec and M 7.1 Puebla-Morelos earthquakes were deep inslab normal-faulting events that caused significant damage to several cen-tral-to-southern regions of Mexico. Inslab earthquakes are an important component of seismicity and seismic hazard in Mexico. Ground-motion prediction equations (GMPEs) are an integral part of seismic...

One important element of understanding basin response to strong shaking is the analysis of spectral ratios, which may provide information about the dominant frequency of ground motion at specific locations. Spectral ratios computed from accelerations recorded by strong-motion stations in Mexico City during the mainshock of the 19 September 2017 M 7...

Ground-motion prediction equations (GMPEs) are critical elements of probabilistic seismic hazard analysis (PSHA), as well as for other applications of ground motions. To isolate the path component for the purpose of building nonergodic GMPEs, we compute a regional GMPE using a large dataset of peak ground accelerations (PGAs) from small-magnitude e...

The Newport-Inglewood/Rose Canyon fault zone (NIRC) is an active strike-slip fault system within the Pacific-North American plate boundary in Southern California, located in close proximity to populated regions of San Diego, Orange, and Los Angeles counties. Prior to this study, the NIRC fault zone's continuity and geometry were not well constraine...

The southern San Andreas fault (SSAF) accommodates a significant amount of strain between the Pacific and North American plates; thus, the fault represents a major geohazard to the populated areas of southern California, in particular the larger Los Angeles metropolitan area. Paleoseismic chronology of ruptures along the SSAF segment suggests this...

The Inner California Borderlands (ICB) is situated off the coast of southern California and northern Baja. The structural and geomorphic characteristics of the area record a middle Oligocene transition from subduction to microplate capture along the California coast.

Faulting in the Inner California Borderlands is complex. In the past, this region has undergone various deformational events such as extensional and rotational deformation and variable strike-slip deformation; this has imparted the geomorphology and fault structures observed offshore Southern California. Several hypotheses have been proposed to exp...

The Inner California Borderlands (ICB) is situated off the coast of southern California and northern Baja. The structural and geomorphic characteristics of the area record a middle Oligocene transition from subduction to microplate capture along the California coast. Marine stratigraphic evidence shows large-scale extension and rotation overprinted...

Geodetic data indicate that faults offshore of Southern California accommodate 6-8 mm/yr of dextral Pacific-North American relative plate motion. In the Inner California Borderlands (ICB), modern strike-slip deformation is overprinted on topography formed during plate boundary reorganization 30-15 Ma. Despite its proximity to urban Southern Califor...

The Inner California Borderlands (ICB) is situated off the coast of southern California and northern Baja. The structural and geomorphic characteristics of the area record a middle Oligocene transition from subduction to microplate capture along the California coast. Marine stratigraphic evidence shows large-scale extension and rotation overprinted...

Geodetic data indicate that faults offshore of Southern California currently accommodate 6-8 mm/yr of dextral Pacific-North American relative plate motion. In the Inner California Borderlands (ICB), modern strike-slip deformation overprints a prominent system of basins and ridges that formed during plate boundary reorganization 30-15 Ma. Despite it...

We investigate interseismic deformation across the San Jacinto fault at Anza, California where previous geodetic observations have indicated an anomalously high shear strain rate. We present an updated set of secular velocities from GPS and InSAR observations that reveal a 2-3 km wide shear zone deforming at a rate that exceeds the background strai...

We performed campaign GPS measurements of near-field interseismic deformation in the Anza section of the San Jacinto fault zone. Our survey occupied 27 benchmarks within 4 km of the fault trace, including a 400-m long alignment array established across the fault in 1990 by SDSU investigators. To constrain the fault slip rate and locking depth, we u...