Fracture Advancing Step Tectonics Observed in the Yuha Desert and Ocotillo, CA, Following the 2010 M_w7.2 El Mayor‐Cucapah Earthquake

Abstract

Uninhabited aerial vehicle synthetic aperture radar (UAVSAR) observations 2009-2017 of the Yuha Desert area and Global Positioning System (GPS) time series encompassing the region reveal a northward migrating pattern of deformation following the 4 April 2010 M w 7.2 El Mayor-Cucapah (EMC) earthquake. The north end of the EMC rupture exhibits an asymmetric pattern of deformation that is substantial and smooth northeast of the rupture and limited but with surface fracturing slip northwest. The earthquake triggered~1 cm of surface coseismic slip at the Yuha fault, which continued to slip postseismically. 2.5 cm of Yuha fault slip occurred by the time of the 15 June 2010 M w 5.7 Ocotillo aftershock and 5 cm of slip occurred by 2017 following a logarithmic afterslip decay 16-day timescale. The Ocotillo aftershock triggered 1.4 cm of slip on a northwest trend extending to the Elsinore fault and by 7 years after the EMC earthquake 2.4 cm of slip had accumulated with a distribution following an afterslip function with a 16-day timescale consistent with other earthquakes and a rate strengthening upper crustal sedimentary layer. GPS data show broad coseismic uplift of the Salton Trough and delayed postseismic motion that may be indicative of fluid migration there and subsidence west of the rupture extension, which continues following the earthquake. The data indicate that the Elsinore, Laguna Salada, and EMC ruptures are part of the same fault system. The results also suggest that north-south shortening and east-west extension across the region drove fracture advancing step tectonics north of the EMC earthquake rupture.Plain Language Summary Airborne radar and Global Positioning System observations of the Yuha Desert and Salton Trough suggest that the 2010 M7.2 El Mayor -Cucapah earthquake rupture, the Laguna Salada fault in Baja California, Mexico, and the Elsinore fault in California are part of the same fault system. The M5.7 Ocotillo aftershock links these faults and is a result of stress propagation from afterslip on the El Mayor -Cucapah rupture. Further east in the Salton Trough fluid migration also contributes to the observed results.

Automated Estimation and Tools to Extract Positions, Velocities, Breaks, and Seasonal Terms From Daily GNSS Measurements: Illuminating Nonlinear Salton Trough Deformation

“…Coseismic displacements or breaks associated with the EMC earthquake have been reported using these tools in Donnellan et al (2018). Here we show two interesting sets of breaks observed post EMC Earth and Space Science earthquake (Figure 3).…”

Buried Aseismic Slip and Off‐Fault Deformation on the Southernmost San Andreas Fault Triggered by the 2010 El Mayor Cucapah Earthquake Revealed by UAVSAR

“…In past work we have reported slip triggered in 2010 on the Imperial, Superstition Hills, and East Elmore Ranch faults, (Donnellan et al, 2014), painstakingly estimated by projected displacements from the UAVSAR interferogram recorded as unwrapped phase. Automatic detection and characterization of surface fracture has been reported (Parker et al, 2018) and estimation of fault slip at depth and fracture zone width is added in Donnellan et al (2018) to track continuing slip on the Yuha fault and the Ocotillo extension of the Elsinore fault over a seven-year period using many interferograms.…”

“…It also reports on the initial detection of coseismic slip on the southern SAF (in line 26514) and estimates coseismic and triggered slip in the 2014 M6.0 South Napa earthquake. A refinement of the method and its application to the estimation of seven years of afterslip on the Yuha Fault and the Laguna Salada-Elsinore transition fault are reported in Donnellan et al (2018).…”

“…A refinement of the method and its application to the estimation of seven years of afterslip on the Yuha Fault and the Laguna Salada‐Elsinore transition fault are reported in Donnellan et al. ( 2018 ).…”

“…Automatic detection and characterization of surface fracture has been reported (Parker et al., 2018 ) and estimation of fault slip at depth and fracture zone width is added in Donnellan et al. ( 2018 ) to track continuing slip on the Yuha fault and the Ocotillo extension of the Elsinore fault over a seven‐year period using many interferograms.…”