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At least 1,423 records · Page 79Linked to original sources
USGS2020

Geologic map of the greater Portland metropolitan area and surrounding region, Oregon and Washington

The Portland-Vancouver-Hillsboro Metropolitan Area (metro area) has great scenic, natural, and cultural resources and is the major economic hub of Oregon. The metro area is subject to a variety of geologic hazards. Underthrusting of the oceanic plate along the Cascadia plate boundary fault, or megathrust, deforms the leading edge of North America and produces earthquakes on the megathrust and in the overlying plate. Rising magma from the deeper parts of the subduction zone produces active volcanoes that form the Cascades Arc, including Mount Hood and Mount St. Helens visible from Portland. Both volcanism and strong ground-shaking from earthquakes have impacted the metro area, most recently in the 1980 eruptions of Mount St. Helens and the 1993 magnitude (M) 5.7 Scotts Mills earthquake. Great offshore earthquakes as large as M 9 on the Cascadia megathrust have shaken the metro area every 500 years or so, most recently in 1700. Giant floods have inundated the metro area, from the ice age Missoula floods about 20,000 to 15,000 years ago to the flood generated by collapse of the Bridge of the Gods landslide dam on the Columbia River around 1421–1447 A.D. Geologic resources of the metro area include the southern part of the Mist Natural Gas Storage Field in the northwest corner of the map area, the Columbia South Shore Well Field aquifer in the Portland Basin, the Columbia River Basalt aquifer of the Tualatin Basin, and the Tualatin Basin Aquifer Storage and Recovery projects. The metro area includes several well-known American Viticultural Areas in the western part of the map area and numerous transportation, electrical transmission, and pipeline corridors. We created this map to provide a uniform, modern geologic database for the greater Portland metro area to better understand its tectonic setting, active faults, volcanoes, landslide hazards, and distribution of geologic materials and resources. Information in this database will be used to improve seismic hazard and resource assessments in this economically important region. NOTE: The sheet 1 map was divided into two parts—sheet 1 (north) and sheet 1 (south)—to facilitate printing and plotting the map.

Oregon, Washington↗
USGS2015

Rates and patterns of surface deformation from laser scanning following the South Napa earthquake, California

The A.D. 2014 M6.0 South Napa earthquake, despite its moderate magnitude, caused significant damage to the Napa Valley in northern California (USA). Surface rupture occurred along several mapped and unmapped faults. Field observations following the earthquake indicated that the magnitude of postseismic surface slip was likely to approach or exceed the maximum coseismic surface slip and as such presented ongoing hazard to infrastructure. Using a laser scanner, we monitored postseismic deformation in three dimensions through time along 0.5 km of the main surface rupture. A key component of this study is the demonstration of proper alignment of repeat surveys using point cloud–based methods that minimize error imposed by both local survey errors and global navigation satellite system georeferencing errors. Using solid modeling of natural and cultural features, we quantify dextral postseismic displacement at several hundred points near the main fault trace. We also quantify total dextral displacement of initially straight cultural features. Total dextral displacement from both coseismic displacement and the first 2.5 d of postseismic displacement ranges from 0.22 to 0.29 m. This range increased to 0.33–0.42 m at 59 d post-earthquake. Furthermore, we estimate up to 0.15 m of vertical deformation during the first 2.5 d post-earthquake, which then increased by ∼0.02 m at 59 d post-earthquake. This vertical deformation is not expressed as a distinct step or scarp at the fault trace but rather as a broad up-to-the-west zone of increasing elevation change spanning the fault trace over several tens of meters, challenging common notions about fault scarp development in strike-slip systems. Integrating these analyses provides three-dimensional mapping of surface deformation and identifies spatial variability in slip along the main fault trace that we attribute to distributed slip via subtle block rotation. These results indicate the benefits of laser scanner surveys along active faults and demonstrate that fine-scale variability in fault slip has been missed by traditional earthquake response methods.

California↗
USGS2023

Least cost path analysis as an objective and automatic method to define the main fault trace for probabilistic fault displacement hazard analyses

A main goal of probabilistic fault displacement hazard analysis (PFDHA) is to quantify displacement along and across an identified active fault that poses a hazard to nearby infrastructure such as roads, bridges, pipelines, and telecommunications. PFDHA relies on empirical models developed using data sets of displacement measurements and mapped surface rupture traces compiled from past global surface rupturing earthquakes by field surveys or remote sensing. However, current approaches to determine the location of the main rupture trace are subjective and lack repeatability due to different geological interpretations of the often complex network of mapped rupture traces. This subjectivity makes it difficult to compile and analyze displacement measurements and ruptures from multiple events in a consistent manner. This study provides an objective and repeatable approach to define a main rupture trace that can be applied to either field or remote sensing data. The new approach defined here can be used in developing rupture trace connectivity and geometry for use in displacement model developments and for use in objectively defining the input fault trace for assessing fault displacement hazard.

Earthquake Spectra↗
USGS2022

Mass wasting along the Cascadia subduction zone: Implications for abyssal turbidite sources and the earthquake record

The only submarine records of large (>M w 7) prehistoric earthquakes along the Cascadia subduction zone are derived from sequences of deep sea turbidites interpreted to represent synchronous, shaking-induced failures along the continental slope. However, the spatial correlation of these deposits along the margin is complicated and the chronological constraints involve significant uncertainties, raising questions about how these deposits were generated. Here we present the most comprehensive spatial database of seafloor failure scarps across the Cascadia margin to date, with more than 8700 features mapped. We observe pervasive mass wasting of the steep lower slope along the ∼800 km length of the margin. This portion of the margin is heavily deformed, uplifted and oversteepened, such that it may be optimally preconditioned to fail during intense shaking events. Our results suggest disintegration of the steep lower slope is likely the primary source of turbidity flows triggered by earthquake shaking in Cascadia. This more proximal source for seismoturbidite generation may be the principal process along subduction margins with steep lower slope topography and may explain why seismoturbidites are found in areas containing few submarine canyons. Furthermore, the extensive mass wasting present on the steep lower slope of central Cascadia, a critical 250 km long section where no records currently exist, suggests additional turbidite records may be found along this portion of the margin by selecting optimal sample sites based on failure patterns. The strong clustering of seafloor failures along the lower slope also suggests the most earthquake intense shaking may be spatially restricted to a narrow zone along the deformation front, which could have important implications for hazard predictions across the region.

California, Oregon, Washington↗
USGS2014

Operational earthquake forecasting can enhance earthquake preparedness

We cannot yet predict large earthquakes in the short term with much reliability and skill, but the strong clustering exhibited in seismic sequences tells us that earthquake probabilities are not constant in time; they generally rise and fall over periods of days to years in correlation with nearby seismic activity. Operational earthquake forecasting (OEF) is the dissemination of authoritative information about these time‐dependent probabilities to help communities prepare for potentially destructive earthquakes. The goal of OEF is to inform the decisions that people and organizations must continually make to mitigate seismic risk and prepare for potentially destructive earthquakes on time scales from days to decades. To fulfill this role, OEF must provide a complete description of the seismic hazard—ground‐motion exceedance probabilities as well as short‐term rupture probabilities—in concert with the long‐term forecasts of probabilistic seismic‐hazard analysis (PSHA).

Seismological Research Letters↗
USGS1978

A preliminary study of the Santa Barbara, California, earthquake of August 13, 1978, and its major aftershocks

The ML5.1 Santa Barbara earthquake of August 13, 1978 occurred at lat 34' 22.2'N., long 119 ? 43.0' 4 km south of Santa Barbara, Calif. at a depth of 12.5 km in the northeast Santa Barbara Channel, part of the western Transverse Ranges geomorphic-structural province. This part of the province is characterized by seismically active, east-trending reverse faults and rates of coastal uplift that have averaged up to about 10 m/1000 years over the last 45,000 years. No surface rupture was detected onshore. Subsurface rupture propagated northwest from the main shock toward Goleta, 15 km west of Santa Barbara, where a maximum acceleration of 0.44 g was measured at ground level and extensive minor damage occurred; only minor injuries were reported. A fairly well-constrained fault-plane solution of the main shock and distribution of the aftershocks indicate that left-reverse-oblique slip occurred on west-northwest-trending, north-dipping reverse faults; inadequate dip control precludes good correlation with any one of several mapped faults. Had the earthquake been larger and rupture propagated to the southeast or a greater distance to the northwest, it could have posed a hazard to oilfield operations. The fault-plane solution and aftershock pattern closely fit the model of regional deformation and the solution closely resembles those of five previously mapped events located within a 15-km radius.

California↗
USGS2005

The orphan tsunami of 1700—Japanese clues to a parent earthquake in North America

Summary A puzzling tsunami entered Japanese history in January 1700. Samurai, merchants, and villagers wrote of minor flooding and damage. Some noted that no parent earthquake had been felt; they were wondering what had set off the waves. They had no way knowing that the tsunami had been spawned during an earthquake along the coast of northwestern North America. This orphan tsunami would not be linked to its parent earthquake until the middle 1990s, through an extraordinary series of discoveries in both North America and Japan. The Orphan Tsunami of 1700 , now in its second edition, tells this scientific detective story through its North American and Japanese clues. The discoveries underpin many of today’s precautions against earthquakes and tsunamis in the Cascadia region of northwestern North America. The Japanese tsunami of March 2011 called attention to those hazards as a mirror image of the transpacific waves of January 1700.

Professional Paper↗
USGS2011

A new strategy for developing Vs 30 maps

Despite obvious limitations as a proxy for site amplification, the use of time-averaged shear-wave velocity over the top 30m (Vs 30 ) is useful and widely practiced, most notably through its use as an explanatory variable in ground motion prediction equations (and thus hazard maps and ShakeMaps, among other applications). Local, regional, and global Vs 30 maps thus have diverse and fundamental uses in earthquake and engineering seismology. As such, we are developing an improved strategy for producing Vs 30 maps given the common observational constraints available in any region for various spatial scales. We investigate a hierarchical approach to mapping Vs 30 , where the baseline model is derived from topographic slope because it is available globally, but geological maps and Vs 30 observations contribute, where available. Using the abundant measured Vs 30 values in Taiwan as an example, we analyze Vs 30 versus slope per geologic unit and observe minor trends that indicate potential interaction of geologic and slope terms. We then regress Vs 30 for the geologic Vs 30 medians, topographic-slope, and cross-term coefficients for a hybrid model. The residuals of this hybrid model still exhibit a strong spatial correlation structure, so we use the kriging-with-a-trend method (the trend is the hybrid model) to further refine the Vs 30 map so as to honor the Vs 30 observations. Unlike the geology or slope models alone, this strategytakes advantage of the predictive capabilities of the two models, yet effectively defaults to ordinary kriging in the vicinity of the observed data, thereby achieving consistency with the observed data.

Book↗
USGS2022

Earthquake scenario development in the 2023 USGS NSHM update

Earthquake scenarios are generally selected to serve a wide variety of local and regional needs ranging from testing a community’s ability to respond to earthquakes to developing proactive targeted mitigation strategies for minimizing impending risk. These deterministic scenarios can also be used to communicate seismic hazard and risk to audiences who are not well versed in more complex methods like probabilistic seismic hazard assessment (PSHA). Accordingly, the U.S. Geological Survey plans to produce a suite of scenarios to accompany the release of the 2023 update to the National Seismic Hazard Model (NSHM). The manuscript describes a preliminary framework for scenario development from hazard and risk/consequence perspectives. Historical seismicity-, hazard-, and consequence-based scenario selection techniques as well as other factors in scenario selection are discussed. The 2023 NSHM scenario development efforts aim to incorporate both hazard and risk considerations while working in close collaboration with local experts and stakeholders.

Conference Paper↗
USGS2022

Paleoseismic study of the XEOLXELEK–Elk Lake fault: A newly identified Holocene fault in thenorthern Cascadia forearc near Victoria, British Columbia, Canada

High-resolution topographic data show a tectonic scarp formed in Quaternary sediments near the city of Victoria in the northern Cascadia forearc on Vancouver Island, British Columbia, Canada. A paleoseismic trench excavation across the structure, the XEOLXELEK–Elk Lake fault, shows evidence for a Holocene (after 12.2 cal ka BP) surface-rupturing reverse-slip earthquake that produced a fault-propagation fold and resulted in the formation of a ∼1.4 to 3.5 m-high scarp. Fault-propagation fold modelling indicates ∼3.2 m of reverse slip on a 50°-dipping fault plane reproduces the observed deformation, and fault-scaling relations suggest a single earthquake rupture with this surface displacement could occur during a ∼Mw 6.1– 7.6 earthquake. Given the fault’s location within the metropolitan area of Victoria, an earthquake near this magnitude would result in significant damage to local infrastructure and this fault is worth considering in future seismic hazard assessments.

Conference Paper↗
USGS1997

Options for the Future of the US National Strong-Motion Program

This report constitutes the requested 'Options Document'. This report considers three options. Option I assumes a constant level of financial support for Operating Expenses (OE) with not additional personnel support. Option II assumes a slight increase in OE support of $150K for FY 99 and beyond. Option III considers the role that a NSMP must play if the nation's urgent need to record the main earthquake at locations of significance for society is to be met. Two parts of Option III are considered. The first part of this option, termed Option III A, considers the role that strong-motion recording in and near man-made structures must play if a near-real time hazard initiative is to be implemented in the United States; The second part of Option III; termed Option III B, considers the scope of a NSMP needed to address society's needs to record the main earthquake in locations of significance for future public earthquake safety.

Open-File Report↗
USGS2023

The Science Application for Risk Reduction (SAFRR) Scenario Retrospective 2006–21

The U.S. Geological Survey Science Application for Risk Reduction (SAFRR) Project has created four major hazard scenarios—ShakeOut, ARkStorm, Tsunami Scenario, and HayWired—with multidisciplinary teams of scientists, academics, and practitioners. By presenting a clear and highly detailed narrative of potential damage from earthquakes, tsunamis, and winter storms, the scenarios are intended to foster science-based preparedness strategies and disaster risk reduction innovations. This evaluation explores the presence of these scenarios in cultures of preparedness and their role in disaster risk reduction, and reports barriers and enablers to creating and using these scenarios. To do this, the evaluation team developed a mixed-methods study that includes background research for each scenario, qualitative interviews, data collection of media and academic engagement, and examples of SAFRR scenario use in hazard planning. The data collection led to the development of a hazard scenario evaluation tool that combines theories from multiple disciplines to create a best practice set of categories that aid in scenario use and efficacy. The evaluation tool categories—actionable, longitudinal, educational, relevant, and thorough—are organized as a series of checklists that are used to determine how the scenario planners prioritized different aspects of the scenarios to achieve their goals. The tool could also be used to aid scenario planning for other regional disaster risk reduction scenarios of a similar scope. Findings from this evaluation include detailed narratives of scenario use over time, demonstrating that the scenarios have continued to be useful in hazard planning and preparedness across the globe. Examples of use include using the scenarios to advocate for resilient building and development policy, to promote hazard response exercises, and as source data for the development of new hazard models and science. The scenarios themselves are innovative, both in the hazard science created for scenario development and in their branding and public engagement as U.S. Geological Survey products. This SAFFR retrospective is a descriptive evaluation and does not formally address the effects of the scenarios. Nevertheless, this report does include evidence of scenario affects as discovered through qualitative interviews and research, which is presented to explore how the SAFRR scenarios have been received by cultures of preparedness.

Scientific Investigations Report↗
USGS2005

Moment tensor inversion of ground motion from mining-induced earthquakes, Trail Mountain, Utah

A seismic network was operated in the vicinity of the Trail Mountain mine, central Utah, from the summer of 2000 to the spring of 2001 to investigate the seismic hazard to a local dam from mining-induced events that we expect to be triggered by future coal mining in this area. In support of efforts to develop groundmotion prediction relations for this situation, we inverted ground-motion recordings for six mining-induced events to determine seismic moment tensors and then to estimate moment magnitudes M for comparison with the network coda magnitudes Mc. Six components of the tensor were determined, for an assumed point source, following the inversion method of McGarr (1992a), which uses key measurements of amplitude from obvious features of the displacement waveforms. When the resulting moment tensors were decomposed into implosive and deviatoric components, we found that four of the six events showed a substantial volume reduction, presumably due to coseismic closure of the adjacent mine openings. For these four events, the volume reduction ranges from 27% to 55% of the shear component (fault area times average slip). Radiated seismic energy, computed from attenuation-corrected body-wave spectra, ranged from 2.4 ?? 105 to 2.4 ?? 106 J for events with M from 1.3 to 1.8, yielding apparent stresses from 0.02 to 0.06 MPa. The energy released for each event, approximated as the product of volume reduction and overburden stress, when compared with the corresponding seismic energies, revealed seismic efficiencies ranging from 0.5% to 7%. The low apparent stresses are consistent with the shallow focal depths of 0.2 to 0.6 km and rupture in a low stress/low strength regime compared with typical earthquake source regions at midcrustal depths.

Bulletin of the Seismological Society of America↗
USGS2006

An assessment of the impact of the 2003 EPRI ground-motion prediction models on the USGS national seismic-hazard maps

Ground-motion attenuation relations have an important impact on seismic hazard analyses. Ground-motion modeling is particularly sensitive to assumptions about wave-propagation attenuation (crustal Q and geometrical spreading), as well as source and site conditions. Studies of path attenuation from earthquakes in eastern North America (ENA) provide insights into the appropriateness of specific attenuation relations. An Electric Power Research Institute (EPRI) (2003, 2004) study combines published ENA ground-motion attenuation relations into four model forms: single-corner, double-corner, hybrid-empirical, and finite-fault. When substituted in the U.S. Geological Survey 2002 national seismic hazard maps for the five ENA relations originally used in those hazard calculations, the EPRI (2003) relations predict similar ground motions and hazard at short periods (<0.5 sec) and significantly lower ground motions (20%-50%) at longer periods (>0.5 sec), relative to the 2002 national maps. A major reason for this difference is due to the crustal seismic-wave attenuation model assumed in a few of the ENA relations combined into the EPRI (2003, 2004) models. Although appropriate differences in geometrical spreading models among ENA relations can also be significant, a few ENA relations have 1-Hz Q-values (Q0) that are below the EPRI (1993) consensus range for Q0 when coupled with a geometrical spreading of R-0.5. The EPRI (2003, 2004) single-corner relation is strongly influenced by the inclusion of ENA relations with assumed Q0 below the EPRI (1993) range, which explains much of the discrepancy in predictions at longer periods.

Bulletin of the Seismological Society of America↗
USGS2019

Using a process-based model of pre-eruptive seismic patterns to forecast evolving eruptive styles at Sinabung Volcano, Indonesia

Most volcanoes worldwide are not monitored in real-time; for those that are, patterns of pre-eruptive earthquakes coupled with conceptual models of magma ascent enable short-term forecasting of eruption onset. Basic event locations, characterization of background seismicity, and recognition of changes in earthquake types and energy release are most important to successful eruption forecasting. During renewed activity at Sinabung volcano, Indonesia, this approach was used by the Center for Volcanology and Geological Hazards Mitigation (CVGHM) and the USGS Volcano Disaster Assistance Program to forecast eruption onset, identify changes in eruptive styles and raise or lower alert levels and extend or contract evacuation zones. After > 400 years of quiescence, Sinabung began erupting in August 2010. The volcano was unmonitored at the onset of these eruptions, which were phreatic, but soon after a monitoring network was installed by CVGHM. Increasing swarms of high-frequency volcano tectonic (VT) earthquakes were used to forecast continuing phreatic eruptions. Volcanic activity decreased in mid-September 2010, while additional intrusions at depth (inferred from continued distal VT swarms) continued through September 2013, when explosive phreatic eruptions recurred. Explosive eruptions were forecast based on increases in real-time seismic amplitude measurement (RSAM) and VT seismicity. Seismicity changed markedly in late November and early December 2013 with the occurrence of deep earthquakes and an overall transition from low-frequency (LF) dominated and irregular (in time and magnitude) earthquakes to more regular LF and hybrid seismicity – a transition that accompanied the continued rise, eventual emergence and growth of a lava dome in the summit crater. This lava dome was first observed on 18 December. In late December 2013 to early January 2014, the eruptive style changed again as additional ascending magma deformed the summit and the dome grew beyond the capacity of the summit crater, resulting in the en masse collapse of the lava dome (2 Mm3) on 11 January and the largest pyroclastic flow to date. The collapse was forecast on the basis of a several order of magnitude increase in RSAM, continued strong distal VT seismicity, an increase in proximal seismicity, and large-scale observed deformation of the summit area. Similarly, a later collapse of a second summit lava dome on 1 February 2014 was forecast on the basis of increased distal seismicity. Here, we demonstrate how a process-based volcano seismicity model was used in combination with real-time data to forecast the time and magnitude of eruptions, as well as changes in eruption style.

Sinabung Volcano↗
USGS2008

Seismic hazard mapping of California incorporating spatial variability of site conditions

The U.S. Geological Survey has recently released a 2008 version of the probabilistic National Seismic Hazard Maps. These maps plot the peak ground acceleration (PGA) and spectral acceleration (SA) ordinates at 0.2 and 1.0 sec with 2% and 10% probabilities of being exceeded in 50 years, corresponding to earthquake return periods of about 2,475 and 475 years, respectively. These acceleration levels were computed for uniform &ldquo;firm rock&rdquo; site conditions, i.e., 760 m/sec average shear-wave velocity in the upper 30 m, and therefore these maps do not show the potential spatial variability of ground motion associated with different site conditions, so we have combined the USGS National Seismic Hazard model with the California showing 17 generalized geologic units geologic units that can be defined by their shear-wave velocity (Wills and Clahan 2006), we regrouped these units into to 7 shear-wave velocities. At each shear-wave velocity value, a probabilistic seismic hazard map was generated for the entire state. By combining seismic hazard maps based on the 7 different shear-wave velocity values, a suite of seismic hazard maps was computed for California for 0.2 and 1.0 sec spectral ordinates at 2% probability of being exceeded in 50 years. The improved maps thus explicitly incorporate the site effects and their spatial variability on ground motion estimates. The SA at 1.0 sec map of seismic shaking potential for California has been now published as California Geological Survey Map Sheet 48, which is intended to be accessible and understandable to the general public.

California↗
USGS2010

A portfolio approach to evaluating natural hazard mitigation policies: An application to lateral-spread ground failure in coastal California

In the past, efforts to prevent catastrophic losses from natural hazards have largely been undertaken by individual property owners based on site—specific evaluations of risks to particular buildings. Public efforts to assess community vulnerability and encourage mitigation have focused on either aggregating site—specific estimates or adopting standards based upon broad assumptions about regional risks. This paper develops an alternative, intermediate—scale approach to regional risk assessment and the evaluation of community mitigation policies. Properties are grouped into types with similar land uses and levels of hazard, and hypothetical community mitigation strategies for protecting these properties are modeled like investment portfolios. The portfolios consist of investments in mitigation against the risk to a community posed by a specific natural hazard. and are defined by a community's mitigation budget and the proportion of the budget invested in locations of each type. The usefulness of this approach is demonstrated through an integrated assessment of earthquake—induced lateral—spread ground failure risk in the Watsonville, California area. Data from the magnitude 6.9 Loma Prieta earthquake of 1989 are used to model lateral—spread ground failure susceptibility. Earth science and economic data are combined and analyzed in a Geographic Information System (CIS). The portfolio model is then used to evaluate the benefits of mitigating the risk in different locations. Two mitigation policies, one that prioritizes mitigation by land use type and the other by hazard zone, are compared with a status quo policy of doing no further mitigation beyond that which already exists. The portfolio representing the hazard zone rule yields a higher expected return than the land use portfolio does; however, the hazard zone portfolio experiences a higher standard deviation. Therefore, neither portfolio is clearly preferred. The two mitigation policies both reduce expected losses and increase overall expected community wealth compared to the status quo policy.

California↗
USGS1996

Use of landslides for paleoseismic analysis

In many environments, landslides preserved in the geologic record can be analyzed to determine the likelihood of seismic triggering. If evidence indicates that a seismic origin is likely for a landslide or group of landslides, and if the landslides can be dated, then a paleo-earthquake can be inferred, and some of its characteristics can be estimated. Such paleoseismic landslide studies thus can help reconstruct the seismic history of a site or region. In regions that contain multiple seismic sources and in regions where surface faulting is absent, paleoseismic ground-failure studies are valuable tools in hazard and risk studies that are more concerned with shaking hazards than with interpretation of the movement histories of individual faults. Paleoseismic landslide analysis involves three steps: (1) identifying a feature as a landslide, (2) dating the landslide, and (3) showing that the landslide was triggered by earthquake shaking. This paper addresses each of these steps and discusses methods for interpreting the results of such studies by reviewing the current state of knowledge of paleoseismic landslide analysis.

Engineering Geology↗