ALBERT

Description: We systematically mapped (scales 〉1:500) the surface rupture of the 4 April 2010 Mw (moment magnitude) 7.2 El Mayor-Cucapah earthquake through the Sierra Cucapah (Baja California, northwestern Mexico) to understand how faults with similar structural and lithologic characteristics control rupture zone fabric, which is here defined by the thickness, distribution, and internal configuration of shearing in a rupture zone. Fault zone thickness and master fault dip are strongly correlated with many parameters of rupture zone fabric. Wider fault zones produce progressively wider rupture zones and both of these parameters increase systematically with decreasing dip of master faults, which varies from 20° to 90° in our dataset. Principal scarps that accommodate more than 90% of the total coseismic slip in a given transect are only observed in fault sections with narrow rupture zones (〈25 m). As rupture zone thickness increases, the number of scarps in a given transect increases, and the scarp with the greatest relative amount of coseismic slip decreases. Rupture zones in previously undeformed alluvium become wider and have more complex arrangements of secondary fractures with oblique slip compared to those with pure normal dip-slip or pure strike-slip. Field relations and lidar (light detection and ranging) difference models show that as magnitude of coseismic slip increases from 0 to 60 cm, the links between kinematically distinct fracture sets increase systematically to the point of forming a throughgoing principal scarp. Our data indicate that secondary faults and penetrative off-fault strain continue to accommodate the oblique kinematics of coseismic slip after the formation of a thoroughgoing principal scarp. Among the widest rupture zones in the Sierra Cucapah are those developed above buried low angle faults due to the transfer of slip to widely distributed steeper faults, which are mechanically more favorably oriented. The results from this study show that the measureable parameters that define rupture zone fabric allow for testing hypotheses concerning the mechanics and propagation of earthquake ruptures, as well as for siting and designing facilities to be constructed in regions near active faults.

Description: Faults in complex tectonic environments interact in various ways, including triggered rupture of one fault by another, that may increase seismic hazard in the surrounding region. We model static and dynamic fault interactions between the strike-slip and thrust fault systems in southern California. We find that rupture of the Sierra Madre-Cucamonga thrust fault system is unlikely to trigger rupture of the San Andreas or San Jacinto strike-slip faults. However, a large northern San Jacinto fault earthquake could trigger a cascading rupture of the Sierra Madre-Cucamonga system, potentially causing a moment magnitude 7.5 to 7.8 earthquake on the edge of the Los Angeles metropolitan region.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Anderson, Greg -- Aagaard, Brad -- Hudnut, Ken -- New York, N.Y. -- Science. 2003 Dec 12;302(5652):1946-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉U.S. Geological Survey, 525 South Wilson Avenue, Pasadena, CA 91106-3212, USA. anderson@unavco.org〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/14671298" target="_blank"〉PubMed〈/a〉

Description: The Landers earthquake, which had a moment magnitude (M(w)) of 7.3, was the largest earthquake to strike the contiguous United States in 40 years. This earthquake resulted from the rupture of five major and many minor right-lateral faults near the southern end of the eastern California shear zone, just north of the San Andreas fault. Its M(w) 6.1 preshock and M(w) 6.2 aftershock had their own aftershocks and foreshocks. Surficial geological observations are consistent with local and far-field seismologic observations of the earthquake. Large surficial offsets (as great as 6 meters) and a relatively short rupture length (85 kilometers) are consistent with seismological calculations of a high stress drop (200 bars), which is in turn consistent with an apparently long recurrence interval for these faults.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Sieh, K -- Jones, L -- Hauksson, E -- Hudnut, K -- Eberhart-Phillips, D -- Heaton, T -- Hough, S -- Hutton, K -- Kanamori, H -- Lilje, A -- Lindvall, S -- McGill, S F -- Mori, J -- Rubin, C -- Spotila, J A -- Stock, J -- Thio, H K -- Treiman, J -- Wernicke, B -- Zachariasen, J -- New York, N.Y. -- Science. 1993 Apr 9;260(5105):171-6.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17807175" target="_blank"〉PubMed〈/a〉

Description: The Gorkha earthquake (magnitude 7.8) on 25 April 2015 and later aftershocks struck South Asia, killing ~9000 people and damaging a large region. Supported by a large campaign of responsive satellite data acquisitions over the earthquake disaster zone, our team undertook a satellite image survey of the earthquakes' induced geohazards in Nepal and China and an assessment of the geomorphic, tectonic, and lithologic controls on quake-induced landslides. Timely analysis and communication aided response and recovery and informed decision-makers. We mapped 4312 coseismic and postseismic landslides. We also surveyed 491 glacier lakes for earthquake damage but found only nine landslide-impacted lakes and no visible satellite evidence of outbursts. Landslide densities correlate with slope, peak ground acceleration, surface downdrop, and specific metamorphic lithologies and large plutonic intrusions.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kargel, J S -- Leonard, G J -- Shugar, D H -- Haritashya, U K -- Bevington, A -- Fielding, E J -- Fujita, K -- Geertsema, M -- Miles, E S -- Steiner, J -- Anderson, E -- Bajracharya, S -- Bawden, G W -- Breashears, D F -- Byers, A -- Collins, B -- Dhital, M R -- Donnellan, A -- Evans, T L -- Geai, M L -- Glasscoe, M T -- Green, D -- Gurung, D R -- Heijenk, R -- Hilborn, A -- Hudnut, K -- Huyck, C -- Immerzeel, W W -- Liming, Jiang -- Jibson, R -- Kaab, A -- Khanal, N R -- Kirschbaum, D -- Kraaijenbrink, P D A -- Lamsal, D -- Shiyin, Liu -- Mingyang, Lv -- McKinney, D -- Nahirnick, N K -- Zhuotong, Nan -- Ojha, S -- Olsenholler, J -- Painter, T H -- Pleasants, M -- Pratima, K C -- Yuan, Q I -- Raup, B H -- Regmi, D -- Rounce, D R -- Sakai, A -- Donghui, Shangguan -- Shea, J M -- Shrestha, A B -- Shukla, A -- Stumm, D -- van der Kooij, M -- Voss, K -- Xin, Wang -- Weihs, B -- Wolfe, D -- Lizong, Wu -- Xiaojun, Yao -- Yoder, M R -- Young, N -- New York, N.Y. -- Science. 2016 Jan 8;351(6269):aac8353. doi: 10.1126/science.aac8353. Epub 2015 Dec 16.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ, USA. kargel@hwr.arizona.edu dshugar@uw.edu uharitashya1@udayton.edu. ; Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ, USA. ; School of Interdisciplinary Arts and Sciences, University of Washington Tacoma, Tacoma, WA, USA. kargel@hwr.arizona.edu dshugar@uw.edu uharitashya1@udayton.edu. ; Department of Geology, University of Dayton, Dayton, OH, USA. kargel@hwr.arizona.edu dshugar@uw.edu uharitashya1@udayton.edu. ; Ministry of Forests, Lands and Natural Resource Operations, Prince George, BC, Canada. ; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA. ; Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan. ; Scott Polar Research Institute, University of Cambridge, Cambridge, UK. ; Institute of Environmental Engineering, Federal Institute of Technology-ETH, Zurich, Switzerland. ; NASA Marshall Space Flight Center, Huntsville, AL, USA. ; International Centre for Integrated Mountain Development, Kathmandu, Nepal. ; NASA Headquarters, Washington, DC, USA. ; GlacierWorks, Marblehead, MA, USA. ; The Mountain Institute, Elkins, WV, USA. ; U.S. Geological Survey, Menlo Park, CA, USA. ; Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal. ; Department of Geography, University of Victoria, Victoria, BC, Canada. ; CVA Engineering, Suresnes, France. ; Earthquake Science Center, U.S. Geological Survey, Pasadena, CA, USA. ; ImageCat, Long Beach, CA, USA. ; Faculty of Geosciences, Utrecht University, Utrecht, Netherlands. ; State Key Laboratory of Geodesy and Earth's Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan, Hubei Province, China. ; U.S. Geological Survey, Golden, CO, USA. ; Department of Geosciences, University of Oslo, Blindern, Oslo, Norway. ; Hydrological Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA. ; Cold and Arid Regions of Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, China. ; School of Earth Sciences and Engineering, Nanjing University, Nanjing, China. ; Department of Civil, Architectural and Environmental Engineering, University of Texas at Austin, Austin, TX, USA. ; School of Geography Science, Nanjing Normal University, Nanjing, China. ; Department of Geography, Texas A&M University, College Station, TX, USA. ; Department of Geology, University of Dayton, Dayton, OH, USA. ; Arizona Remote Sensing Center, School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, USA. ; National Snow and Ice Data Center, University of Colorado, Boulder, CO, USA. ; Himalayan Research Center, Kathmandu, Nepal. ; Environmental and Water Resources Engineering, University of Texas at Austin, Austin, TX, USA. ; Wadia Institute of Himalayan Geology, Dehradun, India. ; MacDonald Dettwiler and Associates-GSI, Ottawa, Ontario, Canada. ; Department of Geography, University of California, Santa Barbara, Santa Barbara, CA, USA. ; College of Architecture and Urban Planning, Hunan University of Science and Technology, Xiangtan, China. ; Geography Department, Kansas State University, Manhattan, KS, USA. ; Global Land Ice Measurements from Space (GLIMS) Steward, Alaska Region, Anchorage, AK, USA. ; College of Geographical Science and Environment, Northwest Normal University, China. ; Department of Physics, University of California, Davis, Davis, CA, USA. ; Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, TAS, Australia.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26676355" target="_blank"〉PubMed〈/a〉

Description: The 25 April 2015 M w  7.8 Gorkha earthquake caused more than 8000 fatalities and widespread building damage in central Nepal. The Italian Space Agency’s COSMO–SkyMed Synthetic Aperture Radar (SAR) satellite acquired data over Kathmandu area four days after the earthquake and the Japan Aerospace Exploration Agency’s Advanced Land Observing Satellite-2 SAR satellite for larger area nine days after the mainshock. We used these radar observations and rapidly produced damage proxy maps (DPMs) derived from temporal changes in Interferometric SAR coherence. Our DPMs were qualitatively validated through comparison with independent damage analyses by the National Geospatial-Intelligence Agency and the United Nations Institute for Training and Research’s United Nations Operational Satellite Applications Programme, and based on our own visual inspection of DigitalGlobe’s WorldView optical pre- versus postevent imagery. Our maps were quickly released to responding agencies and the public, and used for damage assessment, determining inspection/imaging priorities, and reconnaissance fieldwork.

Description: We measured offsets on tectonically displaced geomorphic features along 80 km of the Clark strand of the San Jacinto fault (SJF) to estimate slip-per-event for the past several surface ruptures. We identify 168 offset features from which we make over 490 measurements using B4 light detection and ranging (LiDAR) imagery and field observations. Our results suggest that LiDAR technology is an exemplary supplement to traditional field methods in slip-per-event studies. Displacement estimates indicate that the most recent surface-rupturing event (MRE) produced an average of 2.5–2.9 m of right-lateral slip with maximum slip of nearly 4 m at Anza, a Mw 7.2–7.5 earthquake. Average multiple-event offsets for the same 80 kms are ~5.5??m, with maximum values of 3 m at Anza for the penultimate event. Cumulative displacements of 9–10 m through Anza suggest the third event was also similar in size. Paleoseismic work at Hog Lake dates the most recent surface rupture event at ca. 1790. A poorly located, large earthquake occurred in southern California on 22 November 1800; we relocate this event to the Clark fault based on the MRE at Hog Lake. We also recognize the occurrence of a younger rupture along ~15–20??km of the fault in Blackburn Canyon with ~1.25??m of average displacement. We attribute these offsets to the 21 April 1918 Mw 6.9 event. These data argue that much or all of the Clark fault, and possibly also the Casa Loma fault, fail together in large earthquakes, but that shorter sections may fail in smaller events.Online Material: Topographic contour maps and hillshades generated from B4 LiDAR data, corresponding field photographs, and data tables comparing LiDAR-based and field-based slip measurements for individual geomorphic features along the Clark fault.

Description: The 16 October 1999 Hector Mine earthquake ( M w  7.1) was the first large earthquake for which postearthquake airborne Light Detection and Ranging (LiDAR) data were collected to image the fault surface rupture. In this work, we present measurements of both vertical and horizontal slip along the entire surface rupture of this earthquake based on airborne LiDAR data acquired in April 2000. We examine the details of the along-fault slip distribution of this earthquake based on 255 horizontal and 85 vertical displacements using a 0.5 m digital elevation model derived from the LiDAR imagery. The slip measurements based on the LiDAR dataset are highest in the epicentral region, and taper in both directions, consistent with earlier findings by other works. The maximum dextral displacement measured from LiDAR imagery is 6.60±1.10 m, located about 700 m south of the highest field measurement (5.25±0.85 m). Our results also illustrate the difficulty in resolving displacements smaller than 1 m using LiDAR imagery alone. We analyze slip variation to see if it is affected by rock type and whether variations are statistically significant. This study demonstrates that a postearthquake airborne LiDAR survey can produce an along-fault horizontal and vertical offset distribution plot of a quality comparable to a reconnaissance field survey. Although LiDAR data can provide a higher sampling density and enable rapid data analysis for documenting slip distributions, we find that, relative to field methods, it has a limited ability to resolve slip that is distributed over several fault strands across a zone. We recommend a combined approach that merges field observation with LiDAR analysis, so that the best attributes of both quantitative topographic and geological insight are utilized in concert to make best estimates of offsets and their uncertainties. Online Material: Tables of LiDAR displacement measurements; slip distributions plots; Google Earth index files and locations where displacements were made; LiDAR data files, and access information to view screen captures of the displacement measurements.

Description: Earthquake-related fault slip in the upper hundreds of meters of Earth’s surface has remained largely unstudied because of challenges measuring deformation in the near field of a fault rupture. We analyze centimeter-scale accuracy mobile laser scanning (MLS) data of deformed vine rows within ±300 m of the principal surface expression of the M (magnitude) 6.0 2014 South Napa earthquake. Rather than assuming surface displacement equivalence to fault slip, we invert the near-field data with a model that allows for, but does not require, the fault to be buried below the surface. The inversion maps the position on a preexisting fault plane of a slip front that terminates ~3 to 25 m below the surface coseismically and within a few hours postseismically. The lack of surface-breaching fault slip is verified by two trenches. We estimate near-surface slip ranging from ~0.5 to 1.25 m. Surface displacement can underestimate fault slip by as much as 30%. This implies that similar biases could be present in short-term geologic slip rates used in seismic hazard analyses. Along strike and downdip, we find deficits in slip: The along-strike deficit is erased after ~1 month by afterslip. We find no evidence of off-fault deformation and conclude that the downdip shallow slip deficit for this event is likely an artifact. As near-field geodetic data rapidly proliferate and will become commonplace, we suggest that analyses of near-surface fault rupture should also use more sophisticated mechanical models and subsurface geomechanical tests.

Description: Toppling analysis of a precariously balanced rock (PBR) can provide insight into the nature of ground motion that has not occurred at that location in the past and, by extension, can constrain peak ground motions for use in engineering design. Earlier approaches have targeted 2D models of the rock or modeled the rock–pedestal contact using spring-damper assemblies that require recalibration for each rock. Here, a method to model PBRs in 3D is presented through a case study of the Echo Cliffs PBR. The 3D model is created from a point cloud of the rock, the pedestal, and their interface, obtained using terrestrial laser scanning. The dynamic response of the model under earthquake excitation is simulated using a rigid-body dynamics algorithm. The veracity of this approach is demonstrated through comparisons against data from shake-table experiments. Fragility maps for toppling probability of the Echo Cliffs PBR as a function of various ground-motion parameters, rock–pedestal interface friction coefficient, and excitation direction are presented. These fragility maps indicate that the toppling probability of this rock is low (less than 0.2) for peak ground acceleration (PGA) and peak ground velocity (PGV) lower than 3 m/s 2 and 0.75 m/s, respectively, suggesting that the ground-motion intensities at this location from earthquakes on nearby faults have most probably not exceeded the above-mentioned PGA and PGV during the age of the PBR. Additionally, the fragility maps generated from this methodology can also be directly coupled with existing probabilistic frameworks to obtain direct constraints on unexceeded ground motion at a PBR’s location. Electronic Supplement: Text and figures describing the steps involved in the modeling of precariously balanced rock (PBR)–pedestal geometry, including dense point cloud representation and final 3D model, hazard deaggregation, and toppling probability.

Description: The 4 April 2010 moment magnitude (M w ) 7.2 El Mayor–Cucapah earthquake revealed the existence of a previously unidentified fault system in Mexico that extends ~120 km from the northern tip of the Gulf of California to the U.S.–Mexico border. The system strikes northwest and is composed of at least seven major faults linked by numerous smaller faults, making this one of the most complex surface ruptures ever documented along the Pacific–North America plate boundary. Rupture propagated bilaterally through three distinct kinematic and geomorphic domains. Southeast of the epicenter, a broad region of distributed fracturing, liquefaction, and discontinuous fault rupture was controlled by a buried, southwest-dipping, dextral-normal fault system that extends ~53 km across the southern Colorado River delta. Northwest of the epicenter, the sense of vertical slip reverses as rupture propagated through multiple strands of an imbricate stack of east-dipping dextral-normal faults that extend ~55 km through the Sierra Cucapah. However, some coseismic slip (10–30 cm) was partitioned onto the west-dipping Laguna Salada fault, which extends parallel to the main rupture and defines the western margin of the Sierra Cucapah. In the northernmost domain, rupture terminates on a series of several north-northeast–striking cross-faults with minor offset (〈8 cm) that cut uplifted and folded sediments of the northern Colorado River delta in the Yuha Desert. In the Sierra Cucapah, primary rupture occurred on four major faults separated by one fault branch and two accommodation zones. The accommodation zones are distributed in a left-stepping en echelon geometry, such that rupture passed systematically to structurally lower faults. The structurally lowest fault that ruptured in this event is inclined as shallowly as ~20°. Net surface offsets in the Sierra Cucapah average ~200 cm, with some reaching 300–400 cm, and rupture kinematics vary greatly along strike. Nonetheless, instantaneous extension directions are consistently oriented ~085° and the dominant slip direction is ~310°, which is slightly (~10°) more westerly than the expected azimuth of relative plate motion, but considerably more oblique to other nearby historical ruptures such as the 1992 Landers earthquake. Complex multifault ruptures are common in the central portion of the Pacific North American plate margin, which is affected by restraining bend tectonics, gravitational potential energy gradients, and the inherently three-dimensional strain of the transtensional and transpressional shear regimes that operate in this region.