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Annotated photograph showing the south wall of a trench cut across trace E near its southern end. Logging of this trench reveals that multiple, much larger displacements have occurred at this location in the past. Preliminary paleoseismic interpretations results indicate 3-4 earthquakes. Two key event horizons are denoted by yellow (Event 2) and blue (Event 4) shading. A distinct down-section increase in vertical separation across multiple fractures (red) is observed. In contrast, the 2014 surface rupture was expressed by a vertical down-to-the-left step of 1-3 cm along a single fracture. C-14 dating of these paleo earthquakes is pending. Photograph and interpretation by Gordon Seitz, CGS.
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Executive Summary. Through discussions between the Federal Emergency Management Agency (FEMA) and the U.S. Geological Survey (USGS) following the South Napa earthquake, it was determined that several key decision points would be faced by FEMA for which additional information should be sought and provided by USGS and its partners. This report addres...
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... The ground motions associated with the 2014 earthquake caused widespread damage, especially to masonry buildings on alluvial soils. Surface faulting caused localized damage to roads, buildings and other infrastructure EERI, 2014; Hudnut et al., 2014; Brocher et al., 2015]. Because of its location in the densely populated SFBA and the resulting surface rupture which affected residential neighborhoods, surface rupture associated with the South Napa earthquake was studied in unprecedented detail using a wide range of geophysical, geodetic and geological methods. ...
... Geologists from the U.S. Geological Survey, the California Geological Survey, academia, NASA, consulting firms, and other government agencies quickly responded to the earthquake. Airborne reconnaissance and photography were performed by USGS in cooperation with the California Highway Patrol on August 24 and 25, 2014 [Hudnut et al., 2014]. Google acquired aerial photography on the day of the earthquake, made it available for viewing on Google Earth, and shared orthometrically corrected mosaic images with the USGS [Google, written communication, 2014]. ...
... Geologists identified the location of surface rupture, measured surface slip amount, documented faulting-related surface effects and shared observations through the California Earthquake Clearinghouse [Rosinski et al., 2015]. Airborne laser scanning was performed over the rupture area on October 9, 2014 [Hudnut et al., 2014; www.opentopography.org, 2015, last accessed 12/2015. ...
The Mw 6.0 South Napa earthquake of 24 August 2014 caused slip on several active fault strands within the West Napa Fault Zone (WNFZ). Field mapping identified 12.5 km of surface rupture. These field observations, near-field geodesy and space geodesy together provide evidence for more than ~30 km of surface deformation with a relatively complex distribution across a number of subparallel lineaments. Along a ~7 km section north of the epicenter, the surface rupture is confined to a single trace that cuts alluvial deposits, reoccupying a low-slope scarp. The rupture continued northward onto at least four other traces through subparallel ridges and valleys. Postseismic slip exceeded coseismic slip along much of the southern part of the main rupture trace with total slip one year post-event approaching 0.5 meters at locations where only a few centimeters were measured the day of the earthquake. Analysis of airborne interferometric synthetic aperture radar data provides slip distributions along fault traces, indicates connectivity and extent of secondary traces, and confirms that postseismic slip only occurred on the main trace of the fault, perhaps indicating secondary structures ruptured as coseismic triggered slip. Previous mapping identified the WNFZ as a zone of distributed faulting, and this was generally borne out by the complex 2014 rupture pattern. Implications for hazard analysis in similar settings include the need to consider the possibility of complex surface rupture in areas of complex topography, especially where multiple potentially Quaternary-active fault strands can be mapped. This article is protected by copyright. All rights reserved.
... The experimental results show a strong N-S component of the displacement field ( Fig. 2A), clearly indicating a strike-slip fault mechanism, with an approximately right lateral displacement along a NW-SE trending fault plane, according to the estimated focal mechanism (Fig. 1), and ~340°/165° strike depending on the dip (east-dipping or westdipping, respectively). This is also in agreement with previous works showing a rupture propagating NNW for about 15 Km [Barnhart et al., 2015] and reaching the surface with a maximum slip of about 46 cm near the city of Napa [Hudnut et al., 2014]. Also he E-W component is significant, especially along the southern part of the fault (Fig. 2B). ...
... Also he E-W component is significant, especially along the southern part of the fault (Fig. 2B). Indeed, as pointed out in previous studies [Hudnut et al., 2014;Wei et al., 2015], the fault strike rotates by about 15° counterclockwise from N to S along the rupture, near the sites where slip peaks. In addition, it is worth noting a small, but not negligible, vertical displacement detected in the north-east side of the fault, where a subsidence of about 8 cm occurred (Fig. 2C). ...
... The lack of GPS stations results in a deformation mainly derived from the InSAR data that are not fully suitable in constraining the N-S component due to the orbital configuration. However, the deformation gradient is located close to the city of Napa, where field investigations by Hudnut et al. [2014] revealed a strike rotation that might have led to the estimated pattern. Table 1 provides an evaluation of the performance of the adopted method. ...
Here we propose a method of data integration with the aim to constrain the 3D deformation field induced by a natural or anthropic phenomenon. We exploit SAR and GPS data for evaluating the coseismic displacement map produced by the Mw 6.0 earthquake occurred on August 24th, 2014 southwest of the city of Napa, California, along the San Andreas Fault system. The seismic event caused several damages producing a 15 Km-long rupture through vineyards, roads and even houses.
... The experimental results show a strong N-S component of the displacement field ( Fig. 2A), clearly indicating a strike-slip fault mechanism, with an approximately right lateral displacement along a NW-SE trending fault plane, according to the estimated focal mechanism (Fig. 1), and ~340°/165° strike depending on the dip (east-dipping or westdipping, respectively). This is also in agreement with previous works showing a rupture propagating NNW for about 15 Km [Barnhart et al., 2015] and reaching the surface with a maximum slip of about 46 cm near the city of Napa [Hudnut et al., 2014]. Also he E-W component is significant, especially along the southern part of the fault (Fig. 2B). ...
... Also he E-W component is significant, especially along the southern part of the fault (Fig. 2B). Indeed, as pointed out in previous studies [Hudnut et al., 2014;Wei et al., 2015], the fault strike rotates by about 15° counterclockwise from N to S along the rupture, near the sites where slip peaks. In addition, it is worth noting a small, but not negligible, vertical displacement detected in the north-east side of the fault, where a subsidence of about 8 cm occurred (Fig. 2C). ...
... The lack of GPS stations results in a deformation mainly derived from the InSAR data that are not fully suitable in constraining the N-S component due to the orbital configuration. However, the deformation gradient is located close to the city of Napa, where field investigations by Hudnut et al. [2014] revealed a strike rotation that might have led to the estimated pattern. Table 1 provides an evaluation of the performance of the adopted method. ...
... The experimental results show a strong N-S component of the displacement field ( Fig. 2A), clearly indicating a strike-slip fault mechanism, with an approximately right lateral displacement along a NW-SE trending fault plane, according to the estimated focal mechanism (Fig. 1), and ~340°/165° strike depending on the dip (east-dipping or westdipping, respectively). This is also in agreement with previous works showing a rupture propagating NNW for about 15 Km [Barnhart et al., 2015] and reaching the surface with a maximum slip of about 46 cm near the city of Napa [Hudnut et al., 2014]. Also he E-W component is significant, especially along the southern part of the fault (Fig. 2B). ...
... Also he E-W component is significant, especially along the southern part of the fault (Fig. 2B). Indeed, as pointed out in previous studies [Hudnut et al., 2014;Wei et al., 2015], the fault strike rotates by about 15° counterclockwise from N to S along the rupture, near the sites where slip peaks. In addition, it is worth noting a small, but not negligible, vertical displacement detected in the north-east side of the fault, where a subsidence of about 8 cm occurred (Fig. 2C). ...
... The lack of GPS stations results in a deformation mainly derived from the InSAR data that are not fully suitable in constraining the N-S component due to the orbital configuration. However, the deformation gradient is located close to the city of Napa, where field investigations by Hudnut et al. [2014] revealed a strike rotation that might have led to the estimated pattern. Table 1 provides an evaluation of the performance of the adopted method. ...
In this study the integration of Sentinel-1 InSAR (Interferometric Synthetic Aperture Radar) and GPS (Global Positioning System) data was performed to estimate the three components of the ground deformation field due to the Mw 6.0 earthquake occurred on August 24th, 2014, in the Napa Valley, California, USA. The SAR data were acquired by the Sentinel-1 satellite on August 7th and 31st respectively. In addition, the GPS observations acquired during the whole month of August were analyzed. These data were obtained from the Bay Area Regional Deformation Network, the UNAVCO and the Crustal Dynamics Data Information System online archives. The data integration was realized by using a Bayesian statistical approach searching for the optimal estimation of the three deformation components. The experimental results show large displacements caused by the earthquake characterized by a predominantly NW-SE strike-slip fault mechanism. © 2016 by the authors; licensee Italian Society of Remote Sensing (AIT).
Poor knowledge of how faults slip and distribute deformation in the shallow crust hinders efforts to mitigate hazards where faults increasingly intersect with the expanding global population at Earth’s surface. Here we analyze two study sites along the 2014 M 6.0 South Napa, California, earthquake rupture, each dominated by either co- or post-seismic shallow fault slip. We combine mobile laser scanning (MLS), active-source seismic tomography, and finite element modeling to investigate how deformation rate and mechanical properties of the shallow crust affect fault behavior. Despite four orders-of-magnitude difference in the rupture velocities, MLS-derived shear strain fields are remarkably similar at the two sites and suggest deceleration of the co-seismic rupture near Earth’s surface. Constrained by the MLS and seismic data, finite element models indicate shallow faulting is more sensitive to lithologic layering and plastic yielding than to the presence of fault compliant zones (i.e., regions surrounding faults with reduced stiffness). Although both elastic and elastoplastic models can reproduce the observed surface displacement fields within the uncertainty of MLS data, elastoplastic models likely provide the most reliable representations of subsurface fault behavior, as they produce geologically reasonable stress states and are consistent with field, geodetic, and seismological observations.
We present evidence for multiple fault branches of the West Napa fault zone (WNFZ) based on fault‐zone trapped waves (FZTWs) generated by two explosions that were detonated within the main surface rupture zone produced by the 24 August 2014 Mw 6.0 South Napa earthquake. The FZTWs were recorded by a 15‐kilometer‐long dense (100 m spacing) linear seismic array consisting of 155 4.5‐hertz three‐component seismometers that were deployed across the surface ruptures and adjacent faults in Napa Valley in the summer of 2016. The two explosions were located ∼3.5 km north and ∼5 km south of the 2016 recording array. Prominent FZTWs, with large amplitudes and long wavetrains following the P and S waves, are observed on the seismograms. We analyzed FZTW waveforms in both time and frequency domains to characterize the branching structure of subsurface rupture zones along the WNFZ. The 2014 surface rupture zone was ∼12 km in length along the main trace of the WNFZ, which appears to form an ∼400–600‐meter‐wide low‐velocity waveguide to depths in excess of 5–7 km. Seismic velocities within the main rupture are reduced by 40%–50% relative to the surrounding‐rock velocities. Within 1.5 km of the main trace of the WNFZ, there are at least two subordinate fault traces that formed 3‐ to 6‐kilometer‐long surface breaks during the 2014 mainshock. Our modeling suggests that these subordinate fault traces are also low‐velocity waveguides that connect with the main rupture at depths of ∼2–3 km, forming a flower structure. FZTWs were also recorded at seismic stations across the Carneros fault (CF), which is ∼1 km west of the WNFZ; this suggests that the CF connects with the WNFZ at shallow depths, even though the CF did not experience surface rupture during the 2014 Mw 6.0 mainshock. 3D finite‐difference simulations of recorded FZTWs imply a branching structure along multiple fault strands associated with the WNFZ.
Quantifying near-field displacements can help enable a better understanding of earthquake physics and hazards. To date, established remote sensing techniques have failed to recover subcentimeter-level near-field displacements at the scale and resolution required for shallow fault physical investigations. In this paper, methods are developed to rapidly extract planar parameters, using fast parallel approaches and an alternative registration approach is employed to automatically match the planes extracted from pairwise temporally spaced mobile laser scanning (MLS) and Airborne laser scanning (ALS) data sets along the Napa fault. The features extracted from two temporally spaced point clouds are then used to calculate rigid-body transformation parameters. The production of robust and accurate deformation maps requires the selection of appropriate planar feature extraction and feature mapping criteria. Rigorously propagated point accuracy estimates are employed to produce realistic estimated errors for the transformation parameters. Displacements of each aggregate study area are computed separately from left and right sides of the fault and compared to be within 3 mm of alinement array displacements. Local differential displacements show distinct patterns which, compared to alinement array measurements, were found to agree within the confidence bounds. The findings demonstrate the ability to accurately estimate near-field deformations from repeated MLS or ALS scans of earthquake-prone urban areas. ALS is also used in conjunction with the MLS data sets, illustrating the algorithm's ability to accommodate different LiDAR collection modalities at subcentimeter-level accuracy. The automated planar extraction and registration is an important contribution to the study of near-field earthquake dynamics and can be used as input observations for future geological inversion models.
We present an investigation into different approaches for high-resolution mapping of near-field surface displacement for strike-slip earthquakes. Airborne laser scanning (ALS) and optical imagery are two common sources of earth observation data available to geoscientists for earthquake documentation and studies. Optical image correlation and point cloud differencing techniques are among the most widely used methods for retrieving displacement signals in the near field. We compare the performances of these techniques for estimating near-field deformation using pre and postevent high-resolution ALS and airborne imagery of the August 24, 2014 Mw 6.0 Napa, California earthquake. Estimates of deformation agree with field observations within a decimeter, at the expected accuracy level of the data. We show that the correlation of intensity images from ALS data can unveil the near-field deformation successfully and outperforms optical image correlation in vegetated areas as well as in the absence of geodetic markers (man-made structures). Furthermore, we illustrate that the point clouds generated with structure from motion perform comparably to ALS point clouds for retrieving the displacement signal in unvegetated areas. Overall, we conclude that ALS data are generally better than imagery for estimating near-field deformation regardless of the estimation methodology and that the iterative closest point algorithm was more effective at recovering the displacement signal.
The Pacific-North American plate boundary in California is composed of a 400-km-wide network of faults and zones of distributed deformation. Earthquakes, even large ones, can occur along individual or combinations of faults within the larger plate boundary system. While research often focuses on the primary and secondary faults, holistic study of the plate boundary is required to answer several fundamental questions. How do plate boundary motions partition across California faults? How do faults within the plate boundary interact during earthquakes? What fraction of strain accumulation is relieved aseismically and does this provide limits on fault rupture propagation? Geodetic imaging, broadly defined as measurement of crustal deformation and topography of the Earth’s surface, enables assessment of topographic characteristics and the spatio-temporal behavior of the Earth’s crust. We focus here on crustal deformation observed with continuous Global Positioning System (GPS) data and Interferometric Synthetic Aperture Radar (InSAR) from NASA’s airborne UAVSAR platform, and on high-resolution topography acquired from lidar and Structure from Motion (SfM) methods. Combined, these measurements are used to identify active structures, past ruptures, transient motions, and distribution of deformation. The observations inform estimates of the mechanical and geometric properties of faults. We discuss five areas in California as examples of different fault behavior, fault maturity and times within the earthquake cycle: the M6.0 2014 South Napa earthquake rupture, the San Jacinto fault, the creeping and locked Carrizo sections of the San Andreas fault, the Landers rupture in the Eastern California Shear Zone, and the convergence of the Eastern California Shear Zone and San Andreas fault in southern California. These examples indicate that distribution of crustal deformation can be measured using interferometric synthetic aperture radar (InSAR), Global Navigation Satellite System (GNSS), and high-resolution topography and can improve our understanding of tectonic deformation and rupture characteristics within the broad plate boundary zone.
Capturing and quantifying the world in three dimensions (x,y,z) using light detection and ranging (lidar) technology drives fundamental advances in the Earth and Ecological Sciences (EES). However, additional lidar dimensions offer the possibility to transcend basic 3-D mapping capabilities, including i) the physical time (t) dimension from repeat lidar acquisition and ii) laser return intensity (LRIλ) data dimension based on the brightness of single- or multi-wavelength (λ) laser returns. The additional dimensions thus add to the x,y, and z dimensions to constitute the five dimensions of lidar (x,y,z, t, LRIλ1… λn). This broader spectrum of lidar dimensionality has already revealed new insights across multiple EES topics, and will enable a wide range of new research and applications. Here, we review recent advances based on repeat lidar collections and analysis of LRI data to highlight novel applications of lidar remote sensing beyond 3-D. Our review outlines the potential and current challenges of time and LRI information from lidar sensors to expand the scope of research applications and insights across the full range of EES applications.
