Jessica R. Murray
Jerry L. Svarc
Ellen L. Phillips
Ryan Clayton Turner
Mark Hunter Murray
Todd Ericksen
Kang Wang
Sarah E. Minson
Roland Burgmann
Frederick Pollitz
Kenneth W. Hudnut
Johanna Nevitt
Evelyn Roeloffs
Janis Hernandez
Brian Olson
Benjamin A. Brooks
2020
<p><span>The U.S. Geological Survey’s geodetic response to the 4–5 July 2019 (Pacific time) Ridgecrest earthquake sequence comprised primarily the installation and/or reoccupation of Global Navigation Satellite System (GNSS) monumentation. Our response focused primarily on the United States’ Navy’s China Lake Naval Air Weapons Station base (NAWSCL). This focus was because much of the surface rupture occurred on the NAWSCL and because of NAWSCL access restrictions only permitting Federal and State of California personnel. In total, we measured or are still measuring at 24 sites, 14 of which were on the NAWSCL and, as of this writing, operational. The majority of sites were set up as continuous stations logging at either 1 sample per second or 1 sample per 15 s. Two stations were recording a 200 m cross‐rupture aperture starting </span><span class="inline-formula no-formula-id">∼10 hr</span><span> after the </span><span class="inline-formula no-formula-id">M</span><span> 6.4 event, and they recorded the coseismic displacements of the </span><span class="inline-formula no-formula-id">M</span><span> 7.1. Approximately, 1 hr after the </span><span class="inline-formula no-formula-id">M</span><span> 7.1 event, two new stations were recording a </span><span class="inline-formula no-formula-id">∼200 m</span><span> cross‐rupture aperture of the surface rupture. In the days following, we established the rest of the stations ranging to a distance of </span><span class="inline-formula no-formula-id">∼15 km</span><span> from the </span><span class="inline-formula no-formula-id">M</span><span> 7.1 principal rupture trace. The lack of differential displacement across the </span><span class="inline-formula no-formula-id">M</span><span> 6.4 rupture during the </span><span class="inline-formula no-formula-id">M</span><span> 7.1 event suggests that it did not reactivate the </span><span class="inline-formula no-formula-id">M</span><span> 6.4 plane. The lack of differential cross‐fault displacement for both events suggests that rapid shallow afterslip did not occur at those two locations. The postseismic time series from these stations shows centimeters of horizontal displacement over periods of a few months. They record a mixture of fault‐parallel and fault‐normal displacements that, in conjunction with analysis of more spatially complete Interferometric Synthetic Aperture Radar displacement fields, suggest that both poroelastic and afterslip phenomena occur along the </span><span class="inline-formula no-formula-id">M</span><span> 6.4 and 7.1 rupture planes. Using preliminary data from these and other regional stations, we also explore the Ridgecrest sequence’s effect on regional GNSS time series and the differentiation of long‐term postseismic motions and secular deformation rates. We find that redefining a common‐mode noise filter using different GNSS stations that are assumed to be unaffected by the earthquakes results in small but systematic differences in the regional velocity field estimate.</span></p>
application/pdf
10.1785/0220200007
en
Seismological Society of America
Rapid geodetic observations of spatiotemporally varying postseismic deformation following the Ridgecrest earthquake sequence: The U.S. Geological Survey response
article