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USGS2020

Hybrid broadband ground motion simulation validation of small magnitude earthquakes in Canterbury, New Zealand

Ground motion simulation validation is an important and necessary task toward establishing the efficacy of physics-based ground motion simulations for seismic hazard analysis and earthquake engineering applications. This article presents a comprehensive validation of the commonly used Graves and Pitarka hybrid broadband ground motion simulation methodology with a recently developed three-dimensional (3D) Canterbury Velocity Model. This is done through simulation of 148 small magnitude earthquake events in the Canterbury, New Zealand, region in order to supplement prior validation efforts directed at several larger magnitude events. Recent empirical ground motion models are also considered to benchmark the simulation predictive capability, which is examined by partitioning the prediction residuals into the various components of ground motion variability. Biases identified in source, path, and site components suggest that improvements to the predictive capabilities of the simulation methodology can be made by using a longer high-frequency path duration model, reducing empirical V s 30 -based low-frequency site amplification, and utilizing site-specific velocity models in the high-frequency simulations.

Canterbury↗

USGS2022

National strategy for landslide loss reduction

Executive Summary Landslide hazards are present in all 50 States and most U.S. territories, and they affect lives, property, infrastructure, and the environment. Landslides are the downslope movement of earth materials under the force of gravity. They can occur without any obvious trigger. Widespread or severe landslide events are often driven by such hazards as hurricanes, earthquakes, volcanic eruptions, heavy rain events, flooding, and wildfires. Landslides can also cause their own cascading consequences, such as the spread of hazardous materials or the creation of devastating local tsunamis. This strategy document describes goals and strategic actions of a comprehensive strategy to meet key challenges to reducing the Nation’s risk from landslide hazards equitably and effectively. The document follows the direction of the National Landslide Preparedness Act (Public Law 116–323) by presenting a strategy for addressing landslide hazards, including risk reduction and response. The act directs the Department of the Interior to establish a program that will work with State, Tribal, and local governments as well as with academia, the private sector, community-based groups, and nonprofit organizations to identify landslide hazards and risk and improve communication, coordination, and emergency preparedness, with the objective of reducing landslide losses. As the only Federal program dedicated to landslide hazard science, the U.S. Geological Survey’s Landslide Hazards Program will lead and coordinate many of the efforts described in this strategy document. Landslide hazard risk reduction must be undertaken collectively and collaboratively across the Federal Government. This strategy document will provide a framework for the creation of an interagency management plan that describes the programs, projects, workforce, and budgets required to carry out the national strategy. The strategy outlined in this document presents a vision of how to equitably produce, communicate, and apply landslide data and science to support a broad range of land management, infrastructure, planning, and emergency response decisions. These decisions are made by a variety of actors, including private and nonprofit landholders; State, Tribal, territorial, city, and county planners; emergency managers; engineers; infrastructure managers; Federal agencies and their partners; and community leaders and individuals. Supporting those decisions and reducing the Nation’s vulnerability to landslides requires overcoming three main challenges: (1) gaps in basic information needed to describe and understand landslide occurrence and societal risk, (2) difficulty in accurately mapping and forecasting landslide hazards, and (3) communication and coordination among the many jurisdictions and sectors that have responsibility for and interest in reducing landslide losses. To address those challenges, this strategy document puts forward a series of strategic actions to achieve four goals: Assess: Decision makers have access to detailed, nationwide, and contextually relevant information on landslide hazard and risk. Coordinate: Landslide hazard mitigation, preparedness, response, and recovery efforts are coordinated across Federal, State, Tribal, territorial, and local levels. Plan: Communities and land managers are prepared and able to plan for landslide hazards. Respond: Landslide surveillance, warnings, and responses to events are effective, efficient, equitable, cooperative, and data-driven to protect lives, property, infrastructure, and the environment. These strategic actions focus on expanding the knowledge of societal risk posed by landslides as well as better understanding of where, when, and why they occur. They focus on applying that knowledge to support landslide risk reduction efforts and decisions, including the establishment of new advisory, coordination, and working groups focused on landslide hazard and risk. They take into account that supporting landslide loss reduction decisions also requires new guidance, tools, and training codeveloped with the entities, organizations, and individuals faced with making those decisions. Finally, they address actions needed to support and expand landslide warning information and improve the technical response to landslide emergencies.

Open-File Report↗

USGS2022

Earthquake early warning: Toward modeling optimal protective actions

Over the past few years early earthquake warning systems have been incorporated into earthquake preparation efforts in many locations around the globe. These systems provide an excellent opportunity for advanced warning of ground shaking and other hazards associated with earthquakes. This study aims to optimize this advanced warning for individuals inside a building when the alert is received. A conceptual framework is presented for modeling optimal protective actions during earthquakes when an earthquake early warning system is available to the individual. Various factors impacting the ability of an individual to take protective action are considered for the modeling process.

Conference Paper↗

USGS2018

2018 one‐year seismic hazard forecast for the central and eastern United States from induced and natural earthquakes

This article describes the U.S. Geological Survey (USGS) 2018 one‐year probabilistic seismic hazard forecast for the central and eastern United States from induced and natural earthquakes. For consistency, the updated 2018 forecast is developed using the same probabilistic seismicity‐based methodology as applied in the two previous forecasts. Rates of earthquakes across the United States M ≥ 3.0 "> M ≥ 3.0 grew rapidly between 2008 and 2015 but have steadily declined over the past 3 years, especially in areas of Oklahoma and southern Kansas where fluid injection has decreased. The seismicity pattern in 2017 was complex with earthquakes more spatially dispersed than in the previous years. Some areas of west‐central Oklahoma experienced increased activity rates where industrial activity increased. Earthquake rates in Oklahoma (429 earthquakes of M ≥ 3 "> M ≥ 3 and 4 M ≥ 4 "> M ≥ 4 ), Raton basin (Colorado/New Mexico border, six earthquakes M ≥ 3 "> M ≥ 3 ), and the New Madrid seismic zone (11 earthquakes M ≥ 3 "> M ≥ 3 ) continue to be higher than historical levels. Almost all of these earthquakes occurred within the highest hazard regions of the 2017 forecast. Even though rates declined over the past 3 years, the short‐term hazard for damaging ground shaking across much of Oklahoma remains at high levels due to continuing high rates of smaller earthquakes that are still hundreds of times higher than at any time in the state’s history. Fine details and variability between the 2016–2018 forecasts are obscured by significant uncertainties in the input model. These short‐term hazard levels are similar to active regions in California. During 2017, M ≥ 3 "> M ≥ 3 earthquakes also occurred in or near Ohio, West Virginia, Missouri, Kentucky, Tennessee, Arkansas, Illinois, Oklahoma, Kansas, Colorado, New Mexico, Utah, and Wyoming.

Seismological Research Letters↗

USGS2007

Comprehensive Areal Model of Earthquake-Induced Landslides: Technical Specification and User Guide

This report describes the complete design of a comprehensive areal model of earthquakeinduced landslides (CAMEL). This report presents the design process, technical specification of CAMEL. It also provides a guide to using the CAMEL source code and template ESRI ArcGIS map document file for applying CAMEL, both of which can be obtained by contacting the authors. CAMEL is a regional-scale model of earthquake-induced landslide hazard developed using fuzzy logic systems. CAMEL currently estimates areal landslide concentration (number of landslides per square kilometer) of six aggregated types of earthquake-induced landslides - three types each for rock and soil.

Open-File Report↗

USGS1990

Quaternary geology and geologic hazards of the West Desert Hazardous Industry Area, Tooele County, Utah

The study of Quaternary geology provides information to evaluate geologic conditions and identify geologic constraints on construction in the West Desert Hazardous Industry Area (WDHIA). The WDHIA includes portions of the Great Salt Lake Desert to the west, underlain by several thousand feet of sediments capped by saline mudflats, and Ripple Valley to the east, separated from the Desert by the Grayback Hills and underlain by several hundred feet of sediments in the Cedar Mountains piedmont zone. Quaternary surficial units include marginal, shore-zone, and deep-water lacustrine sediments deposited in Pleistocene Lake Bonneville; eolian deposits; and alluvial sediments. The level of Lake Bonneville underwent major oscillations resulting in the creation of four basin-wide shorelines, three of which are recognized in the WDHIA. Geologic hazards in the WDHIA include the possible contamination of ground water in basin-fill aquifers, debris flows and flash floods in the piedmont zone, and earthquakes and related hazards. Numerous factors contribute to unsafe foundation conditions. Silty and sandy sediments may be subject to liquefaction or hydrocompaction, clayey sediments and mud flats of the Great Salt Lake Desert may be subject to shrinking or swelling, and gypsiferous dunes and salt flats are subject to subsidence due to dissolution.

Conference Paper↗

USGS2014

Predicting the spatial extent of liquefaction from geospatial and earthquake specific parameters

T he spatially extensive damage from the 2010-2011 Christchurch, New Zealand earthquake events are a reminder of the need for liquefaction hazard maps for anticipating damage from future earthquakes. Liquefaction hazard mapping as traditionally relied on detailed geologic mapping and expensive site studies. These traditional techniques are difficult to apply globally for rapid response or loss estimation. We have developed a logistic regression model to predict the probability of liquefaction occurrence in coastal sedimentary areas as a function of simple and globally available geospatial features (e.g., derived from digital elevation models) and standard earthquake-specific intensity data (e.g., peak ground acceleration). Some of the geospatial explanatory variables that we consider are taken from the hydrology community, which has a long tradition of using remotely sensed data as proxies for subsurface parameters. As a result of using high resolution, remotely-sensed, and spatially continuous data as a proxy for important subsurface parameters such as soil density and soil saturation, and by using a probabilistic modeling framework, our liquefaction model inherently includes the natural spatial variability of liquefaction occurrence and provides an estimate of spatial extent of liquefaction for a given earthquake. To provide a quantitative check on how the predicted probabilities relate to spatial extent of liquefaction, we report the frequency of observed liquefaction features within a range of predicted probabilities. The percentage of liquefaction is the areal extent of observed liquefaction within a given probability contour. The regional model and the results show that there is a strong relationship between the predicted probability and the observed percentage of liquefaction. Visual inspection of the probability contours for each event also indicates that the pattern of liquefaction is well represented by the model.

Conference Paper↗

USGS2021

2021 U.S. National Seismic Hazard Model for the State of Hawaii

The 2021 U.S. National Seismic Hazard Model (NSHM) for the State of Hawaii updates the two-decades-old former model by incorporating new data and modeling techniques to improve the underlying ground shaking forecasts of tectonic-fault, tectonic-flexure, volcanic, and caldera collapse earthquakes. Two earthquake ground shaking hazard models (public policy and research) are produced that differ in how they account for declustered catalogs. The earthquake source model is based on (1) declustered earthquake catalogs smoothed with adaptive smoothing methods, (2) earthquake rate forecasts based on three temporally varying 60-year time periods, (3) maximum magnitude models that extend to larger earthquakes than previously considered, (4) a separate Kīlauea-specific seismogenic caldera collapse model which accounts for clustered event behavior observed during the 2018 eruption, and (5) fault ruptures that consider historic seismicity, GPS-based strain rates, and a new Quaternary fault database. Two new Hawaii-specific ground motion models (GMMs) and five additional global models consistent with Hawaii shaking data are used to forecast ground shaking at 23 spectral periods and peak parameters. Site effects are modeled using western U.S. and Hawaii specific empirical equations and provide shaking forecasts for eight site classes. For most sites the new model results in similar spectral accelerations as those in the 2001 NSHM, with a few exceptions caused mostly by GMM changes. Ground motions are highest in the southern portion of the Island of Hawai‘i due to high rates of forecasted earthquakes on décollement faults. Shaking decays to the northwest where lower earthquake rates result from flexure of the tectonic plate. Large epistemic uncertainties in source characterizations and GMMs lead to an overall high uncertainty (more than a factor of 3) in ground shaking at Honolulu and Hilo. The new shaking model indicates significant chances of slight or greater damaging ground motions across most of the island chain.

Hawai'i↗

USGS2019

California’s exposure to volcanic hazards

The potential for damaging earthquakes, landslides, floods, tsunamis, and wildfires is widely recognized in California. The same cannot be said for volcanic eruptions, despite the fact that they occur in the state about as frequently as the largest earthquakes on the San Andreas Fault. At least ten eruptions have taken place in the past 1,000 years, and future volcanic eruptions are inevitable. The U.S. Geological Survey’s (USGS) national volcanic threat assessment identifies eight young volcanic areas in California as moderate, high, or very high threat. Of the eight volcanic areas that exist in California, molten rock resides beneath at least seven of these—Medicine Lake volcano, Mount Shasta, Lassen Volcanic Center, Clear Lake volcanic field, the Long Valley volcanic region, Coso volcanic field, and Salton Buttes—and are therefore considered “active” volcanoes producing volcanic earthquakes, toxic gas emissions, hot springs, geothermal systems, and (or) ground movement. The USGS California Volcano Observatory in Menlo Park, California, monitors these potentially hazardous volcanoes to help communities and government authorities understand, prepare for, and respond to volcanic activity. Although volcanic activity can sometimes be forecast, eruptions, like earthquakes or tsunamis, cannot be prevented. Understanding the hazards and identifying what and who is in harm’s way is the first step in mitigating volcanic risk and building community resilience to volcanic hazards. This report, which was prepared in collaboration with the California Governor’s Office of Emergency Services and the California Geological Survey, provides a broad perspective on the state’s exposure to volcanic hazards by integrating volcanic hazard information with geospatial data on at-risk populations, infrastructure, and resources. This information is intended to prompt site- and sector-specific vulnerability analyses and preparation of hazard mitigation and response plans.

California↗

USGS2018

Overview of the geologic effects of the November 14, 2016, Mw 7.8 Kaikoura, New Zealand, earthquake

The November 14, 2016, Kaikoura, New Zealand, earthquake (moment magnitude [Mw] 7.8) triggered more than 10,000 landslides over an area of about 12,000 square kilometers in the northeastern part of the South Island of New Zealand. In collaboration with GNS Science (the Institute of Geological and Nuclear Science Limited), we conducted ground and helicopter reconnaissance of the affected areas and assisted in rapid hazard evaluation. The majority of the triggered landslides were shallow- to moderate-depth (1–10 meters), highly disrupted falls and slides in rock and debris from Lower Cretaceous graywacke sandstone in the Seaward Kaikoura Range. Deeper, more coherent landslides in weak Upper Cretaceous to Neogene sedimentary rock also were numerous in the gentler topography south and inland (west) of the Seaward Kaikoura Range. The principal ground-failure hazards from the earthquake were the hundreds of valley-blocking landslides, many of which impounded lakes and ponds that posed potential downstream flooding hazards. Both large and small landslides also blocked road and rail corridors in many locations, including the main north-south highway (State Highway 1), which was still closed in October 2017. As part of our investigation, we compared post-earthquake field observations to the output of models used to estimate near-real-time landslide probabilities following earthquakes. The models generally over-predicted landslide occurrence and thus need further refinement.

Kaikoura↗

USGS2013

Serious games experiment toward agent-based simulation

We evaluate the potential for serious games to be used as a scientifically based decision-support product that supports the United States Geological Survey’s (USGS) mission--to provide integrated, unbiased scientific information that can make a substantial contribution to societal well-being for a wide variety of complex environmental challenges. Serious or pedagogical games are an engaging way to educate decisionmakers and stakeholders about environmental challenges that are usefully informed by natural and social scientific information and knowledge and can be designed to promote interactive learning and exploration in the face of large uncertainties, divergent values, and complex situations. We developed two serious games that use challenging environmental-planning issues to demonstrate and investigate the potential contributions of serious games to inform regional-planning decisions. Delta Skelta is a game emulating long-term integrated environmental planning in the Sacramento-San Joaquin Delta, California, that incorporates natural hazards (flooding and earthquakes) and consequences for California water supplies amidst conflicting water interests. Age of Ecology is a game that simulates interactions between economic and ecologic processes, as well as natural hazards while implementing agent-based modeling. The content of these games spans the USGS science mission areas related to water, ecosystems, natural hazards, land use, and climate change. We describe the games, reflect on design and informational aspects, and comment on their potential usefulness. During the process of developing these games, we identified various design trade-offs involving factual information, strategic thinking, game-winning criteria, elements of fun, number and type of players, time horizon, and uncertainty. We evaluate the two games in terms of accomplishments and limitations. Overall, we demonstrated the potential for these games to usefully represent scientific information within challenging environmental and ecosystem-management contexts and to provide an interactive way of learning about the complexity of interactions between people and natural systems. Further progress on the use of pedagogical games to fulfill the USGS mission will require collaboration among scientists, game developers, educators, and stakeholders. We conclude that as the USGS positions itself to communicate and convey the results of multiple science strategies, including natural-resource security and sustainability, pedagogical game development and agent-based modeling offer a means to (1) establish interdisciplinary and collaborative teams with a focused integrated outcome; (2) contribute to the modeling of interaction, feedback, and adaptation of ecosystems; and (3) enable social learning through a broadly appealing and increasingly sophisticated medium.

Open-File Report↗

USGS2023

Uncertainties in intensity-based earthquake magnitude estimates

Estimating the magnitude of historical earthquakes is crucial for assessing seismic hazard. Magnitudes of early‐instrumental earthquakes can be inferred using a combination of instrumental records, field observations, and the observed distribution of shaking intensity determined from macroseismic observations. For earthquakes before 1900, shaking intensity distributions often provide the only information to constrain earthquake magnitude. Considerable effort has been made to develop methods to estimate the magnitude of moderate‐to‐large historical earthquakes using shaking intensities derived from macroseismic data. In this study, we consider earthquakes in California with known instrumental magnitudes to explore uncertainties in estimating the magnitude of historical earthquakes from intensity information alone. We use three California‐specific intensity prediction equations (IPEs) and an IPE based on a global ground‐motion model (GMM) to determine optimum intensity‐based magnitudes for 33 moderate‐to‐large California earthquakes between 1979 and 2021. Intensity‐based magnitudes are close to instrumental magnitudes on average. However, intensity‐based magnitudes for individual events differ by as much as 2.2 magnitude units from instrumental magnitudes. This result reflects the weak dependence of ground motions and shaking intensities on moment magnitude and their strong dependence on stress drop. Considering the intensity distributions of the 1906 San Francisco and 1989 Loma Prieta earthquakes, we show that information that could constrain rupture length is discarded when considering only the 2D decay of intensity with distance. We also show that ground‐motion intensity conversion equations used in a GMM‐based approach may cause a systematic overestimation of large historical earthquake magnitudes. This study underscores both the reducible and potentially irreducible uncertainties associated with using intensity data to estimate magnitudes of historical earthquakes using IPEs and highlights the value of using additional information to constrain rupture dimensions. Using intensity observations alone, moment magnitude uncertainties are typically on the order of a full unit.

California↗

USGS2005

Real-time forecasts of tomorrow's earthquakes in California

Despite a lack of reliable deterministic earthquake precursors, seismologists have significant predictive information about earthquake activity from an increasingly accurate understanding of the clustering properties of earthquakes. In the past 15 years, time-dependent earthquake probabilities based on a generic short-term clustering model have been made publicly available in near-real time during major earthquake sequences. These forecasts describe the probability and number of events that are, on average, likely to occur following a mainshock of a given magnitude, but are not tailored to the particular sequence at hand and contain no information about the likely locations of the aftershocks. Our model builds upon the basic principles of this generic forecast model in two ways: it recasts the forecast in terms of the probability of strong ground shaking, and it combines an existing time-independent earthquake occurrence model based on fault data and historical earthquakes with increasingly complex models describing the local time-dependent earthquake clustering. The result is a time-dependent map showing the probability of strong shaking anywhere in California within the next 24 hours. The seismic hazard modelling approach we describe provides a better understanding of time-dependent earthquake hazard, and increases its usefulness for the public, emergency planners and the media.

Nature↗

USGS2014

Seismic‐wave attenuation determined from tectonic tremor in multiple subduction zones

Tectonic tremor provides a new source of observations that can be used to constrain the seismic attenuation parameter for ground‐motion prediction and hazard mapping. Traditionally, recorded earthquakes of magnitude ∼3–8 are used to develop ground‐motion prediction equations; however, typical earthquake records may be sparse in areas of high hazard. In this study, we constrain the distance decay of seismic waves using measurements of the amplitude decay of tectonic tremor, which is plentiful in some regions. Tectonic tremor occurs in the frequency band of interest for ground‐motion prediction (i.e., ∼2–8 Hz) and is located on the subducting plate interface, at the lower boundary of where future large earthquakes are expected. We empirically fit the distance decay of peak ground velocity from tremor to determine the attenuation parameter in four subduction zones: Nankai, Japan; Cascadia, United States–Canada; Jalisco, Mexico; and southern Chile. With the large amount of data available from tremor, we show that in the upper plate, the lower crust is less attenuating than the upper crust. We apply the same analysis to intraslab events in Nankai and show the possibility that waves traveling from deeper intraslab events experience more attenuation than those from the shallower tremor due to ray paths that pass through the subducting and highly attenuating oceanic crust. This suggests that high pore‐fluid pressure is present in the tremor source region. These differences imply that the attenuation parameter determined from intraslab earthquakes may underestimate ground motion for future large earthquakes on the plate interface.

Cascadia↗

USGS1978

Reconnaissance engineering geology of the Petersburg area, southeastern Alaska, with emphasis on geologic hazards

A program to study the engineering geology of most larger Alaska coastal communities and to evaluate their earthquake and other geologic hazards was started following the 1964 Alaska earthquake; this report about the Petersburg area is a product of that program. Field-study methods were of a reconnaissance nature, and thus, interpretations in the report are tentative. Landscape of the northern end of Mitkof Island on which Petersburg is situated is characterized by a gently sloping, muskeg-covered terrain, with altitudes mostly less than 30 m. In contrast, much of the rest of the island is composed of mountainous terrain with many steep valleys. During the Pleistocene Epoch, the Petersburg area presumably was covered by ice several times; glaciers deeply eroded many valleys on Mitkof Island and adjacent areas. The last major deglaciation probably was largely completed by 12,000 years ago. Delayed rebound of the earth's crust, after the melting of large amounts of ice, permitted extensive inundation of land in the Petersburg area. Subsequently, emergence has elevated marine deposits to a present-day altitude of at least 65 m and probably to 75 m. Bedrock in the Petersburg map area is composed of relatively hard metamorphic rocks, chiefly phyllite and probably some graywacke. Rocks are of Middle(?) Jurassic to Early Cretaceous age. Five types of surficial geologic material of Quaternary age were recognized: (1) mixed deposits consisting of diamicton, silt-clay, and sand or sandy pebble gravel, (2) alluvial deposits, (3) shore and delta deposits, (4) organic deposits, and (5) artificial fill. Geologic structure in southeastern Alaska is complex because several cycles of tectonic deformation since at least early Paelozoic time have affected different parts of the region. The latest of the major tectonic events in southeastern Alaska occurred in Tertiary time, with some minor activity continuing into the Quaternary Period. Along the outer coast of southeastern Alaska, active strike-slip movement is occurring along the Chichagof-Baranof and Queen Charlotte faults. A segment of the prominent Coast-Range lineament, part of which may be a fault, lies 18 km northeast of Petersburg. Many earthquakes occur along the outer coast of southeastern Alaska. Most of these shocks are associated with movements along the Chichagof-Baranof, Queen Charlotte, and Transition faults. A few small earthquakes occur in the region between the outer coast and the southern part of the Coast Mountains. 0nly a few earthquakes have been recorded as felt at Petersburg; these shocks and others possibly felt in the Petersburg region are tabulated. Among the recorded earthquakes the highest intensity (about V-VI) as the magnitude 7.1 earthquake of October 24, 1927, that occurred probably along the Chichagof-Baranof fault, and about 225 km northwest of Petersburg; damage was reported as minor. Other large earthquakes along the Chichagof-Baranof fault that affected or probably affected the Petersburg area in a minor way occurred on August 22, 1949 (magnitude 8.1) and on July 30, 1972 (magnitude 7.25). From a consideration of the tectonics and earthquake history of the region, earthquakes similar to the 1927, 1949, and 1972 shocks are expected to recur on segments of the Chichagof-Baranof or Queen Charlotte faults. The closest of these fault segments is about 170 km southwest from Petersburg. The likelihood of destructive earthquakes being generated along faults closer to Petersburg is unknown. A very generalized discussion of possible geologic effects that could occur in the area during a postulated, theoretically reasonable worst case earthquake of magnitude 8 occurring along the outer coast about 170 km southwest from Petersburg notes that ground shaking probably would be strongest on organic deposits and least on bedrock and on firm, compact diamicton. Among other effects that could happen are: (1) liquefaction of some of the few delta and alluvial

Open-File Report↗

USGS2008

Landslide hazard mitigation in North America

Active landslides throughout the states and territories of the United States result in extensive property loss and 25-50 deaths per year. The U.S. Geological Survey (USGS) has a long history of detailed examination of landslides since the work of Howe (1909) in the San Juan Mountains of Colorado. In the last four decades, landslide inventory maps and landslide hazard maps have depicted landslides of different ages, identified fresh landslide scarps, and indicated the direction of landslide movement for different regions of the states of Colorado, California, and Pennsylvania. Probability-based methods improve landslide hazards assessments. Rainstorms, earthquakes, wildfires, and volcanic eruptions can trigger landslides. Improvements in remote sensing of rainfall make it possible to issue landslide advisories and warnings for vulnerable areas. From 1986 to 1995, the USGS issued hazard warnings based on rainfall in the San Francisco Bay area. USGS workers also identified rainfall thresholds triggering landslides in Puerto Rico, Hawaii, Washington, and the Blue Ridge Mountains of central Virginia. Detailed onsite monitoring of landslides near highways in California and Colorado aided transportation officials. The USGS developed a comprehensive, multi-sector, and multi-agency strategy to mitigate landslide hazards nationwide. This study formed the foundation of the National Landslide Hazards Mitigation Strategy. The USGS, in partnership with the U.S. National Weather Service and the State of California, began to develop a real-time warning system for landslides from wildfires in Southern California as a pilot study in 2005.

Environmental & Engineering Geoscience↗

USGS2011

Selected Images of the Effects of the October 15, 2006, Kiholo Bay-Mahukona, Hawai'i, Earthquakes and Recovery Efforts

Early on the morning of October 15, 2006, two moderate earthquakes—the largest in decades—struck the Island of Hawai‘i. The first of these, which occurred at 7:07 a.m., HST (1707 UTC), was a magnitude ( M ) 6.7 earthquake, centered beneath Kīholo Bay on the northwestern coast of the island (19.878°N, 155.935°W), at a depth of 39 km. The second earthquake, which struck 6 minutes, 24 seconds later, at 7:14 a.m., HST (1714 UTC), was located 28 km to the north-northwest of Kīholo Bay (20.129°N, 155.983°W), centered at a depth of 19 km. This M 6.0 earthquake has since been referred to as the Māhukona earthquake. Losses from the combined effects of these earthquakes are estimated to be $200 million—the most costly events, by far, in Hawai‘i’s earthquake history. Although the vast majority of earthquakes in the State of Hawaii are closely related to the active volcanism associated with the southeastern part of the Island of Hawai‘i, the October 2006 Kīholo Bay and Māhukona earthquakes clearly suggest the devastating potential of deeper lithospheric earthquakes. Large earthquakes thought to be nearly M 7 have struck near the islands of Lāna‘i (1871) and Maui (1938). It is thought that these, like the 2006 earthquakes, were deep lithospheric flexure earthquakes (Wyss and Koyanagi, 1992; Klein and others, 2001). Thus, it is important to recognize the potential seismic hazard posed by such earthquakes beneath the older Hawaiian Islands. The data and observations afforded by the 2006 earthquakes promise to improve probabilistic seismic hazards modeling in Hawai‘i. The effects of the October 15, 2006, Kīholo Bay-Māhukona earthquakes are shown in images taken from the coastal route along the northern half of the Island of Hawai‘i, where damage was the most concentrated. The direction of presentation is counter-clockwise, from Pa‘auilo on the eastern or windward (Hāmākua) side to Kealakekua Bay on the western or leeward (Kona) side. A list of sites, their locations, coordinates, and distance from the epicenter at Kīholo Bay are given in table 1. A Google Earth map (fig. 7) and a topographic map (fig. 8) pinpoint the 36 sites where damage was documented and digital images were compiled for this collection.

Data Series↗

USGS1978

FRISK: computer program for seismic risk analysis using faults as earthquake sources

This computer program makes probabilistic seismic hazard calculations at sites affected by earthquakes occurring on faults which are defined by the user as a series of line segments. The length of rupture of the fault as a function of earthquake magnitude is accounted for, and ground motion estimates at the site are made using the magnitude of the earthquake and the closest distance from the site to the rupture zone. Uncertainty in the earthquake magnitude, in the rupture given magnitude, in the location of the rupture zone on the fault, in the maximum possible magnitude of earthquakes, and in the ground motion at the site given the earthquake, its size, rupture length, and location, are accounted for explicitly. FRISK (Fault RISK) was written to take advantage of repeated calculations, so that seismic hazard analyses for several ground motion parameters (for instance, peak ground acceleration, velocity, and displacement), and for several sites, are most efficiently made with one execution of the program rather than with repeated executions. The program uses a step-truncated exponential distribution for earthquake magnitude, a lognormal distribution for rupture length given magnitude, a uniform distribution for rupture location on faults, and a lognormal distribution of site amplitude given magnitude of the earthquake and distance from the rupture zone to the site. The program has been structured so that other functions may easily be substituted if this is appropriate for a particular problem; for example a wide range of deterministic or probabilistic geophysical models for estimating ground motion may be incorporated, and the program will yield probabilistic estimates of seismic hazard.

Open-File Report↗