Hayward Fault Research Articles

Ground-motions site and event specificity: Insights from assessing a suite of simulated ground motions in the San Francisco Bay Area

This article presents the results of a research that is part of a larger collaborative effort between the Lawrence Berkeley National Laboratory and the Pacific Earthquake Engineering Research Center, funded by the US Department of Energy Office of Cybersecurity, Energy Security and Emergency Response. The main objective of this study is to assess a suite of near and far-field simulated ground motions obtained from 20 realizations of an M7 Hayward Fault earthquake in the San Francisco Bay Area, California USA, and inform the selection of rupture simulation parameters leading to strong motions. To this aim, comparisons are conducted with NGA-W2 and directivity ground-motion models and a selected population of records. An archetypal steel moment-resisting frame is utilized to assess infrastructure response distributions. The analyses carried out for each simulated event and subdomain with consistent properties in terms of shallow shear-wave velocity proved to be instrumental for better interpreting the differences between simulated motions and empirical models. The main reasons identified for variances between simulations and empirical relationships included (1) directivity effects fully captured by the simulations across the full breadth of rupture models; (2) site vicinity to ruptures that incorporate large-slip patches, particularly if these are in the forward-directivity direction; and (3) presence of geologic structures that can “trap” seismic waves and produce ground motions with large amplitude and long signal duration. The analyses carried out in this work provide a path for interpreting ground-motion site and event specificity obtained from a suite of physics-based simulations, differing only in the rupture model characterization, to inform the selection of simulation scenarios for site-specific engineering analyses under strong excitations. Evidence from this work points to the possibility that current hazard models may underestimate ground-motion intensities in areas where the combined effect of directivity and site conditions results in large ground-motion amplitudes.

Vulnerability of suspension bridges to spatially variable vertical ground motions

This study investigates the vulnerability of long-span suspension bridges to spatially variable vertical ground motions (SV-VGMs). While of recognized importance, a comprehensive understanding of this topic has been traditionally limited by the unavailability of an adequate number of arrays of motions. In this work, 10 simulations of a large-magnitude Hayward Fault earthquake are utilized to perform site-specific structural response assessments of a suspension bridge under different load scenarios. A detailed nonlinear model representative of the West San Francisco-Oakland Bay Bridge is employed as the case study structure. Four sets of nonlinear time-history analyses are performed with and without VGMs and with and without the incorporation of spatial variability to offer the basis for a complete comparison of the demand distributions across different load cases. Results indicate that VGMs largely influence the response of the bridge decks in the vertical direction, with an increase in drifts up to 2× for the case of synchronous input and up to 2.5× for the case of asynchronous inputs. The analysis of the bridge response in the time and frequency domain across all load cases reveals a high sensitivity of the decks’ response to minor time lags in input motions of comparable amplitude, which are seen to activate the contribution of higher modes to the structural response. Evidence from this study points to the potential of severely underestimating structural demands if the (even limited) spatial variability of the input motions is not incorporated correctly. For the case study structure, the probability of exceeding the onset of nonlinearity in the short decks at the design earthquake level is seen to increase by a factor of about two when considering SV-VGMs as opposed to synchronous horizontal motions only.

Upper crustal seismic velocity structure of the Hayward fault zone, San Francisco Bay, California, USA: Results from the 2016 East Bay Seismic Experiment (EBSI-16)

We developed Vp, Vs, Vp/Vs ratio, and Poisson’s ratio models of the uppermost crust (<4 km depth) from the eastern San Francisco (SF) Bay (California, USA) to near the Calaveras fault along a 15-km-long, linear profile. Upper crustal velocities are highly variable beneath, west, and well east of the Hayward fault. We observe eight notable features, from west to east: (1) Near San Francisco Bay, there is an ∼2-km-wide structure with high Vp/Vs ratios (up to 5) and Poisson’s ratios (up to 0.48) extending from the surface to the base of our model, which we suggest the structure is a near-vertical fault that lies along a straight-line projection between the Silver Creek fault to the south and the Point Richmond fault to the north. The structure may be part of an ∼90-km-long fault along the eastern SF Bay. (2) The western East Bay Plain, the lower lying area between the bay and the hills, includes up to 800 m of low-velocity sediments (Vp ∼1600−3000 m/s, Vs ∼500 m/s to ∼1000 m/s), underlain by higher velocity basement rocks (Vp ∼3000−5800 m/s; Vs ∼1000−1500 m/s). (3) Between ∼1 km and 3 km east of the Bay shoreline, sediments thin in a series of steps (likely faults) toward the Hayward fault. (4) Between ∼3 km west and ∼1 km east of the Hayward fault (at the East Chabot fault) at depths greater than 1 km, basement Vp (up to 6000 m/s) and Vs (up to 2800 m/s) are high, and Vp/Vs ratios (<2) and Poisson’s ratios (<0.3) are low, suggesting crystalline rocks. Furthermore, a near-vertical zone of low Vp/Vs ratios and Poisson’s ratios is between near-surface traces of the Hayward and East Chabot faults, likely corresponding to the San Leandro Gabbro of Ponce et al. (2003). (5) Eastward of the East Chabot fault in the upper 1.5 km, basement Vp (∼3000 m/s to ∼4200 m/s) and Vs (∼1200−2000 m/s) are lower than those west of the fault. (6) In the eastern Hayward/Oakland Hills, there are zones of laterally varying, high- and low-velocity (Vp ∼2500−3000 m/s) Jurassic−Cretaceous and Tertiary sediments in the shallow subsurface that likely extend much deeper than imaged. (7) Seismic energy that propagates westward from sources east of the Hayward fault (HF) appear weaker than energy that propagates eastward from sources west of the HF, suggesting that the HF acts as a partial barrier to shallow seismic energy propagation into the more populated eastern SF Bay area. (8) Unlike many fault zones, it appears that the active trace of the Hayward fault (in our study area) is not cored by a prominent, low-velocity zone relative to rocks to the east and west of the active trace. However, the active trace does mark a prominent change from relatively higher velocities to the west and lower velocities to the east.

Modeling post-disaster recovery: Accounting for rental and multi-family housing

Post-disaster housing recovery models increase our understanding of recovery dynamics, vulnerable populations, and how people are affected by the direct losses that disasters create. Past recovery models have focused on single-family owner-occupied housing, while empirical evidence shows that rental units and multi-family housing are disadvantaged in post-disaster recovery. To fill this gap, this article presents an agent-based housing recovery model that includes the four common type–tenure combinations of single- and multi-family owner- and renter-occupied housing. The proposed model accounts for the different recovery processes, emphasizing funding sources available to each type–tenure. The outputs of our model include the timing of financing and recovery at building resolution across a community. We demonstrate the model with a case study of Alameda, California, recovering from a simulated M7.0 earthquake on the Hayward fault. The processes in the model replicate higher non-recovery of multi-family housing than single-family housing, as observed in past disasters, and a heavy reliance of single-family renter-occupied units on Small Business Administration funding, which is expected due to low earthquake insurance penetration. The simulation results indicate that multi-family housing would have the highest portion of unmet need remaining; however, some buildings with unmet needs are anticipated to be able to obtain a large portion of their funding. The remaining portion may be filled using personal financing or may be overcome with downsizing or downgrades. Multi-family housing would also benefit the most from Community Development Block Grants for Disaster Recovery (CDBG-DR). This benefit is a result of modeling the financing sources, that CDBG-DR is available, and that many multi-family buildings do not qualify for other sources. Communities’ allocation of public funding is important for housing recovery. Our model can help inform and compare potential financing policies to allocate public funds.

ASCE/SEI 7‐compliant site‐specific evaluation of the seismic demand posed to reinforced concrete buildings with real and simulated ground motions

AbstractState‐of‐the‐art seismic design and assessment methodologies rely on the utilization of ground‐motion records scaled to site‐specific risk‐targeted spectra to perform nonlinear time‐history analyses and estimate mean structural demands. Motivated by the discrepancies in structural response estimates resulting from different selection and scaling methods, this study assesses the implications of utilizing site‐specific simulated ground motions from 3‐D physics‐based wave‐propagation models as opposed to historical records from worldwide catalogs in ASCE/SEI7‐compliant procedures for seismic performance evaluations. A suite of validated realizations of an M7 Hayward Fault earthquake in the San Francisco Bay Area and two modern reinforced concrete moment‐resisting frame buildings are utilized as a case study. The 2014 USGS earthquake hazard and probability maps are employed for the hazard calculations, and the PEER NGA‐West2 database is used for the selection of the real ground motions. The building models are coupled with the simulated and real ground motions to perform a total of 30,552 nonlinear time‐history analyses. Structural demands obtained from real and simulated motions are examined and compared at the regional‐scale in terms of peak interstory drift ratio median and dispersion, and localization along the building height. The correlations between observed structural responses and ground‐motion features are discussed to potentially inform current code‐compliant methodologies for ground‐motion selection. Results show that utilizing site‐specific simulated ground motions that incorporate path, fault geometry, and site‐condition effects as opposed to historical ground‐motion records may lead to differences in the structural demands above 50%. Such differences are highly spatially variable throughout the region and difficult to predict.

Arrest of the Mw 6.8 January 24, 2020 Elaziğ (Turkey) earthquake by shallow fault creep

It has long been conjectured that creeping sections of strike slip faults arrest or subdue earthquake rupture, partly because of their reduced slip potential and partly because of their velocity-strengthening frictional properties. However, no instrumentally recorded large earthquake (Mw ≥ 6.8) on any well instrumented continental strike-slip fault has thus far occurred that has clearly been arrested at a region of fault creep, rendering it difficult to identify experimentally the parameters that control rupture arrest. Nearfield GPS, InSAR and creepmeter data from the 2020 Elazığ (Turkey) earthquake reveal not only how rupture propagation of a large earthquake is hindered by shallow creep reducing the earthquake size, but also provide important quantitative insights into the late interseismic, coseismic and post seismic behavior of a creeping fault, which has important implications for evaluating hazard potential of a major earthquake on a creeping fault, such as has been forecast for the Hayward fault in California.

Seismogenic Patches in a Tectonic Fault Interface

Tectonic faults show rheological heterogeneity in interfaces, and the spectrum of their sliding regimes span a continuum from the slow-slip events to dynamic ruptures. The heterogeneity of the fault interface is crucial for the mechanics of faulting. By using the earthquake source locations, the complex structure of a fault interface can be reproduced at a resolution down to 50–100 m. Here, we use a declustered seismic catalog of Northern California to investigate structures of 11 segments of San Andreas, Calaveras, and Hayward faults. The cumulative length of all the segments is about 500 km. All the selected segments belong to subvertical strike–slip faults. A noticeable localization of sources near the fault cores is observed for all segments. The projection of earthquake sources to the fault plane shows severe inhomogeneity. Topologically dense clusters (seismogenic patches (SPs)) can be detected in fault planes. The longer the observation are, the more distinct are the clusters. The SPs usually cover about 10%–20% of the fault interface area. It is in the vicinity of SPs that earthquakes of magnitudes above 5 are usually initiated. The Voronoi tessellation is used to determine the orderliness of SPs. Distributions of areas of Voronoi cells of all the SPs obey the lognormal law, and the value of Voronoi entropy of 1.6–1.9 prevails. The findings show the informativeness of the background seismicity in revealing the heterogenous structure of a tectonic fault interface.

Nodal Seismic Experiment at the Berkeley Section of the Hayward Fault

AbstractThe Hayward fault (HF) in the San Francisco Bay area of California is one of the most hazardous faults of the San Andreas fault system with a total length of 70 km. In November 2020, we conducted a dense array experiment that deployed 182 three-component nodal sensors for about a five-week period at the Berkeley section of the HF. Our primary goal of this experiment was to image the seismic velocity structure in the upper crust of this area to better understand the fault-zone structure and its elastic properties. A linear array (10 stations with 5–10 m spacing) was deployed on the north side of University of California, Berkeley Memorial Stadium where the HF runs underneath, together with 27 stations that were installed surrounding the stadium. Here we detail our scientific motivation, station metadata, and quality of seismic waveforms. We also show initial results of fault-zone guided waves observed from the linear array and provide first-step results of Green’s functions between nodal stations obtained by an ambient noise cross-correlation analysis.

Monitoring creep along the Hayward Fault using structure-from-motion photogrammetry of offset curbs

SUMMARY We present observations of sidewalk curbs that are offset by creep on the Hayward Fault in Fremont, CA. Using structure-from-motion photogrammetry techniques, we construct 3-D models from suites of 2-D photos taken from 2015 to 2018 at 20 sites along the fault. By aligning and comparing these models, we measure the 3-D displacements of each offset sidewalk through time at precisions of ∼0.5 mm yr−1. We find that on average individual offset curbs record <40 per cent of the overall creep rate measured at nearby alignment arrays (which span a fault-perpendicular distance of 100 m or more). The ‘fault trace’ can more accurately be considered a zone of deformation, narrower than an alignment array width but wider than one curb length (∼3–5 m). Sites for which we have multiple time intervals to compare show interannual temporal variability in creep rate and direction. Our methods offer a new, complementary approach to cheaply and efficiently document creep-related deformation in an urban setting, one that may be particularly useful for tracking deformation of engineered materials and their cohesion to the subsurface. Given the use of readily available equipment (consumer-grade camera, GPS, ruler), ease of data collection and accessibility of urban field sites, we believe that this style of monitoring would lend itself particularly well to citizen science efforts.

Marine Paleoseismic Evidence for Seismic and Aseismic Slip Along the Hayward‐Rodgers Creek Fault System in Northern San Pablo Bay

AbstractDistinguishing between seismic and aseismic fault slip in the geologic record is difficult, yet fundamental to estimating the seismic potential of faults and the likelihood of multi‐fault ruptures. We integrated chirp sub‐bottom imaging with targeted cross‐fault coring and core analyses of sedimentary proxy data to characterize vertical deformation and slip behavior within an extensional fault bend along the Hayward‐Rodgers Creek fault system in northern San Pablo Bay. We identified and traced four key seismic horizons (R1–R4), all younger than approximately 1400 CE, that cross the fault and extend throughout the basin. A stratigraphic age model was developed using detailed down‐core radiocarbon and radioisotope dating combined with measurements of anthropogenic metal concentrations. The onset of hydraulic mining within the Sierra Nevada in 1852 CE left a clear geochemical and magnetic signature within core samples. This key time horizon was used to calculate a local reservoir correction and reduce uncertainty in radiocarbon age calibration and models. Vertical fault offset of strata younger than the most recent surface‐rupturing earthquake on the Hayward fault in 1868 CE suggest near‐surface vertical creep is occurring along the fault in northern San Pablo Bay at a rate of approximately 0.4 mm/yr. In addition, we present evidence of at least one and possibly two coseismic events associated with growth strata above horizons R1 and R2, with median event ages estimated to be 1400 CE and 1800 CE, respectively. The timing of both these events overlaps with paleoseismic events on adjacent fault sections, suggesting the possibility of multi‐fault rupture.

Monitoring aseismic fault creep using persistent urban geodetic markers generated from mobile laser scanning

High resolution and high accuracy distributed detection of fault creep deformation remains challenging given limited observations and associated change detection strategies. A mobile laser scanning-based change detection method that is capable of measuring centimeter-level near-field (<150 m from fault) deformation is described. The methodology leverages the use of man-made features in the built environment as geodetic markers that can be temporally tracked. The proposed framework consists of a RANSAC-based corresponding plane detector and a combined least squares displacement estimator. Using repeat mobile laser scanning data collected in 2015 and 2017 on a 2 ​km segment of the Hayward fault, near-field fault creep displacement and non-linear creep deformation are estimated. The detection results reveal 2.5 ​± ​1.5 ​cm of accumulated fault parallel creep displacement in the far-field. The laser scanning estimates of displacement match collocated alinement array observations at the 4 ​mm level in the near field. The proposed change detection framework is shown to be accurate and practical for fault creep displacement detection in the near field and the detected non-linear creep displacement patterns will help elucidate the complex physics of surface faulting.

A Simplified Method for Rapid Estimation of Emergency Water Supply Needs after Earthquakes

Researchers are investigating the problem of estimating households with potable water service outages soon after an earthquake. Most of these modeling approaches are computationally intensive, have large proprietary data collection requirements or lack precision, making them unfeasible for rapid assessment, prioritization, and allocation of emergency water resources in large, complex disasters. This study proposes a new simplified analytical method—performed without proprietary water pipeline data—to estimate water supply needs after earthquakes, and a case study of its application in the HayWired earthquake scenario. In the HayWired scenario—a moment magnitude (Mw) 7.0 Hayward Fault earthquake in the San Francisco Bay Area, California (USA)—an analysis of potable water supply in two water utility districts was performed using the University of Colorado Water Network (CUWNet) model. In the case study, application of the simplified method extends these estimates of household water service outage to the nine counties adjacent to the San Francisco Bay, aggregated by a ~250 m2 (nine-arcsecond) grid. The study estimates about 1.38 million households (3.7 million residents) out of 7.6 million residents (2017, ambient, nighttime population) with potable water service outage soon after the earthquake—about an 8% increase from the HayWired scenario estimates.

Conditioned Simulation of Ground-Motion Time Series at Uninstrumented Sites Using Gaussian Process Regression

ABSTRACTGround-motion time series are essential input data in seismic analysis and performance assessment of the built environment. Because instruments to record free-field ground motions are generally sparse, methods are needed to estimate motions at locations with no available ground-motion recording instrumentation. In this study, given a set of observed motions, ground-motion time series at target sites are constructed using a Gaussian process regression (GPR) approach, which treats the real and imaginary parts of the Fourier spectrum as random Gaussian variables. Model training, verification, and applicability studies are carried out using the physics-based simulated ground motions of the 1906 Mw 7.9 San Francisco earthquake and Mw 7.0 Hayward fault scenario earthquake in northern California. The method’s performance is further evaluated using the 2019 Mw 7.1 Ridgecrest earthquake ground motions recorded by the Community Seismic Network stations located in southern California. These evaluations indicate that the trained GPR model is able to adequately estimate the ground-motion time series for frequency ranges that are pertinent for most earthquake engineering applications. The trained GPR model exhibits proper performance in predicting the long-period content of the ground motions as well as directivity pulses.

Engineering evaluation of the EQSIM simulated ground‐motion database: The San Francisco Bay Area region

AbstractGround‐motion simulations for infrequent earthquake scenarios are gaining increasing interest in the engineering community for their potential to inform performance‐based structural design and assessment, particularly in regions where major earthquakes are expected, but recordings from consistent historical events are not available. However, the absence of empirical data makes the evaluation of such scenarios and the interpretation of the simulation results very challenging. In this context, this paper presents the evaluation of the first EQSIM (v.1.1.0) ground‐motion simulations generated for the San Francisco Bay Area (SFBA) region. The current database, which is at the first stages of development, includes eight realizations of a Hayward Fault Mw7 event. The evaluation of the simulated motions is first conducted on the average ground‐motion amplitudes through comparison against the NGA‐W2 GMPEs and a selected population of real records. A methodology for selecting a population of real records consistent with the simulated event is proposed. The objective of the proposed evaluation is twofold: (1) build confidence in the realistic character of the simulated motions for their use in engineering applications and (2) offer a critical physics‐based interpretation of the simulation results that can help improve key features of the simulation models. To further investigate the implications of using the simulated ground motions for site‐specific structural assessments, the ASCE7‐16 approach is employed for the analysis of two hazard‐consistent near‐field sites in the SFBA. Results are discussed. This study offers a critical review of the EQSIM (v.1.1.0) SFBA ground‐motion simulations and suggestions for improving the earthquake rupture models.

Eikonal equation-basedP-wave seismic azimuthal anisotropy tomography of the crustal structure beneath northern California

SUMMARYDelineating spatial variations of seismic anisotropy in the crust is of great importance for the understanding of structural heterogeneities, regional stress regime and ongoing crustal dynamics. In this study, we present a 3-D anisotropic P-wave velocity model of the crust beneath northern California by using the eikonal equation-based seismic azimuthal anisotropy tomography method. The velocity heterogeneities under different geological units are well resolved. The thickness of the low-velocity sediment at the Great Valley Sequence is estimated to be about 10 km. The high-velocity anomaly underlying Great Valley probably indicates the existence of ophiolite bodies. Strong velocity contrasts are revealed across the Hayward Fault (2–9 km) and San Andreas Fault (2–12 km). In the upper crust (2–9 km), the fast velocity directions (FVDs) are generally fault-parallel in the northern Coast Range, which may be caused by geological structure; while the FVDs are mainly NE–SW in Great Valley and the northern Sierra Nevada possibly due to the regional maximum horizontal compressive stress. In contrast, seismic anisotropy in the mid-lower crust (12–22 km) may be attributed to the alignment of mica schists. The anisotropy contrast across the San Andreas Fault may imply different mechanisms of crustal deformation on the two sides of the fault. Both the strong velocity contrasts and the high angle (∼45° or above) between the FVDs and the strikes of faults suggest that the faults are mechanically weak in the San Francisco bay area (2–6 km). This study suggests that the eikonal equation-based seismic azimuthal anisotropy tomography is a valuable tool to investigate crustal heterogeneities and tectonic deformation.

A Geology and Geodesy Based Model of Dynamic Earthquake Rupture on the Rodgers Creek‐Hayward‐Calaveras Fault System, California

AbstractThe Hayward fault in California's San Francisco Bay area produces large earthquakes, with the last occurring in 1868. We examine how physics‐based dynamic rupture modeling can be used to numerically simulate large earthquakes on not only the Hayward fault, but also its connected companions to the north and south, the Rodgers Creek and Calaveras faults. Equipped with a wealth of images of this fault system, including those of its 3D geology and 3D geometry, in addition to inferences about its interseismic creep‐rate pattern and rock‐friction behavior, we use a finite‐element computer code to perform 3D dynamic earthquake rupture simulations. We find that the rock properties affect the locations and amount of slip produced in our simulated large earthquakes. Crucial factors that control rupture behavior in our modeling are the earthquake nucleation locations, the fault geometry, and the data that reveal where the fault system is creeping or locked. Our findings suggest that large Rodgers Creek‐Hayward‐Calaveras‐Northern Calaveras (RC‐H‐C‐NC) fault‐system earthquakes may result from dynamic rupture that starts in a locked part of the fault system, but is then stopped by the creeping parts, leading to high‐magnitude‐6 earthquakes; or, from dynamic rupture that starts in a locked part of the fault system, then cascades through some of the creeping parts, leading to magnitude‐7 earthquakes.

Regional Ground-Motion Simulation Using Recorded Ground Motions

ABSTRACT Regional ground-motion simulation is important for postearthquake seismic damage assessment. Herein, a ground-motion simulation method using recorded ground motions is proposed. Inverse-distance-weighted interpolation of the response spectra is performed to obtain the response spectrum at the target location. Then the ground-motion time history for the target location is obtained by correcting the nearest-station records using the continuous wavelet transform. An evaluation measure for the accuracy of the predicted ground motion, that is, the response-spectrum error, is introduced, and its relationship with the seismic damage of regional buildings is determined via a city-scale nonlinear time-history analysis. The response-spectrum errors under different site conditions, distances, and elevation differences are analyzed. The application conditions for the proposed method are subsequently outlined. The Tsinghua campus is examined as a case study to validate the method. Finally, downtown San Francisco under an Mw 7.0 simulated earthquake on the Hayward fault is selected as an example to demonstrate the proposed method. The proposed method overcomes the difficulties in determining the intrastation ground motions and provides valuable input to postearthquake seismic damage assessment.

Regional-Scale 3D Ground-Motion Simulations of Mw 7 Earthquakes on the Hayward Fault, Northern California Resolving Frequencies 0–10 Hz and Including Site-Response Corrections

ABSTRACTLarge earthquake ground-motion simulations in 3D Earth models provide constraints on site-specific shaking intensities but have suffered from limited frequency resolution and ignored site response in soft soils. We report new regional-scale 3D simulations for moment magnitude 7.0 scenario earthquakes on the Hayward Fault, northern California with SW4. Simulations resolved significantly broader band frequencies (0–10 Hz) than previous studies and represent the highest resolution simulations for any such earthquake to date. Seismic waves were excited by a kinematic rupture following Graves and Pitarka (2016) and obeyed wave propagation in a 3D Earth model with topography from the U.S. Geological Survey (USGS) assuming a minimum shear wavespeed, VSmin, of 500 m/s. We corrected motions for linear and nonlinear site response for the shear wavespeed, VS, from the USGS 3D model, using a recently developed ground-motion model (GMM) for Fourier amplitude spectra (Bayless and Abrahamson, 2018, 2019a). At soft soil locations subjected to strong shaking, the site-corrected intensities reflect the competing effects of linear amplification by low VS material, reduction of stiffness during nonlinear deformation, and damping of high frequencies. Sites with near-surface VS of 500 m/s or greater require no linear site correction but can experience amplitude reduction due to nonlinear response. Averaged over all sites, we obtained reasonable agreement with empirical ergodic median GMMs currently used for seismic hazard and design ground motions (epsilon less than 1), with marked improvement at soft sedimentary sites. At specific locations, the simulated shaking intensities show systematic differences from the GMMs that reveal path and site effects not captured in these ergodic models. Results suggest how next generation regional-scale earthquake simulations can provide higher spatial and frequency resolution while including effects of soft soils that are commonly ignored in scenario earthquake ground-motion simulations.

Documenting Aftermath: Information Infrastructures in the Wake of Disasters by Megan Finn

Reviewed by: Documenting Aftermath: Information Infrastructures in the Wake of Disasters by Megan Finn Scott Gabriel Knowles (bio) Documenting Aftermath: Information Infrastructures in the Wake of Disasters. By Megan Finn. Cambridge, MA: MIT Press, 2018. Pp. 280. Hardcover $39. A disaster is a disruption of the expected order of events, and that disruption is mediated by information technology. What we most need to know—but what the disruption often obscures from us—are the names of the injured and dead, the sites of greatest danger, and the commands of government officials working to restore safety. In her valuable new volume Documenting Aftermath, Megan Finn develops a set of earthquake history case studies through which to explore the crucial dimensions of "information infrastructures." The theoretical apparatus of the book revolves around two crucial concepts. First are the "information orders": "institutions, technologies, and practices that might characterize how societies produce and share documents" (p. 3). These information orders provide the social and material context for the possibilities of knowing any given event (a disaster in this case). Flowing from this first and more general concept is a sharper historical analytic, the "information infrastructure": both material and relational, this infrastructure is comprised of the "ongoing processes involved in the production and circulation of documents" (p. 6). Finn is especially attentive to the public dimensions of information infrastructures and the ways they frame the political struggles of a particular time and place. She takes as a given the social construction of information and technology in her theorization, looking constantly for places where the intended function of a technological system, from the telegraph to a disaster action plan, is modified according to the identities of users and the material facts on the ground. In the end, we must see the information order as a "site of contention over which accounts of an event are treated authoritatively" (p. 151). With her analytical project defined, Finn looks across time to see how these "public information infrastructures" behave in different disasters. She wants to "consider how the public information infrastructure after each earthquake did or did not recover" (p. 157). In this, Finn is writing in [End Page 704] the historiographic tradition established by crucial works like Carl Smith's Urban Disorder and the Shape of Belief (1995) and Christine Meisner Rosen's The Limits of Power (2003), and updated by recent works like Joanna Dyl's Seismic City (2017). From a disaster studies perspective, this temporal gallivanting is essential. It shows how disasters in different times and places consistently defy the emergency-managerial imperatives like clear lines of authority and communication. Finn argues that in the earthquake cases she surveys, "the dominant institutions tended to stay dominant in times of disaster, as people came up with interesting work-arounds to enable the continuity of public information infrastructures. The technologies and practices that people use regularly are also the technologies and practices that they lean on in times of disaster" (p. 158). Disasters, then, don't represent extrahistorical breaks from an imagined normal life in which a new world is constructed out of the rubble. One fascinating continuity across time is the perception of time lag in the making and dispensation of postdisaster information. In the case of the 1868 Hayward Fault Earthquake, and again after the 1906 San Francisco Earthquake, this problem showed up in the challenge of establishing an authoritative account of damage due to the disruption of telegraphic service. Newspapers scrambled to publish special editions, but damage to the telegraph network slowed reporting. For individuals, telegraphic offices served as sites of information-seeking, but they failed to deliver messages with the rapidity customers expected—many thousands of messages were finally carried via the postal service. Finn describes with narrative skill and in close detail the public outcry when it was learned that "telegrams were not delivered by the wires but instead were physically transported across the country by boat and train" (p. 61). This failure of infrastructure revealed in both 1868 and certainly by 1906 just how accustomed Americans were to near-instantaneous information connectivity—its deprivation and the anxiety caused by the lack of information about loved ones provoked a second disaster after the...

The Effect of Fault Geometry and Minimum Shear Wavespeed on 3D Ground-Motion Simulations for an Mw 6.5 Hayward Fault Scenario Earthquake, San Francisco Bay Area, Northern California

AbstractWe investigated the effects of fault geometry and assumed minimum shear wavespeed (VSmin) on 3D ground-motion simulations (0–2.5 Hz) in general, using a moment magnitude (Mw) 6.5 earthquake on the Hayward fault (HF). Simulations of large earthquakes on the northeast-dipping HF using the U.S. Geological Survey (USGS) 3D seismic model have shown intensity asymmetry with stronger shaking for the Great Valley Sequence east of the HF (hanging wall) relative to the Franciscan Complex to the west (footwall). We performed simulations with three fault geometries in both plane-layered (1D) and 3D models. Results show that the nonvertical fault geometries result in larger motions on the hanging wall relative to the vertical fault for the same Earth model with up to 50% amplifications in single-component peak ground velocity (PGV) within 10 km of the rupture. Near-fault motions on the footwall are reduced for the nonvertical faults, but less than they are increased on the hanging wall. Simulations assuming VSmin values of 500 and 250 m/s reveal that PGVs are on average 25% higher west of the HF when using the lower VSmin, with some locations amplified by a factor of 3. Increasing frequency content from 2.5 to 5 Hz increases PGV values. Spectral ratios of these two VSmin cases show average amplifications of 2–4 (0.5–1.5 Hz) for the lower VSmin west of the fault. Large differences (up to 2×) in PGV across the HF from previous studies persist even for the case with a vertical fault or VSmin of 250 m/s. We conclude that assuming a VSmin of 500 m/s underestimates intensities west of the HF for frequencies above 0.5 Hz, and that low upper crustal (depth &amp;lt;10 km) shear wavespeeds defined in the 3D model contribute most to higher intensities east of the HF.