El Mayor-Cucapah (M_w7.2) earthquake: Early near-field postseismic deformation from InSAR and GPS observations

Abstract

El Mayor-Cucapah earthquake occurred on 4 April 2010 in northeastern Baja California just south of the U.S.-Mexico border. The earthquake ruptured several previously mapped faults, as well as some unidentified ones, including the Pescadores, Borrego, Paso Inferior and Paso Superior faults in the Sierra Cucapah, and the Indiviso fault in the Mexicali Valley and Colorado River Delta. We conducted several Global Positioning System (GPS) campaign surveys of preexisting and newly established benchmarks within 30 km of the earthquake rupture. Most of the benchmarks were occupied within days after the earthquake, allowing us to capture the very early postseismic transient motions. The GPS data show postseismic displacements in the same direction as the coseismic displacements; time series indicate a gradual decay in postseismic velocities with characteristic time scales of 66 ± 9 days and 20 ± 3 days, assuming exponential and logarithmic decay, respectively. We also analyzed interferometric synthetic aperture radar (InSAR) data from the Envisat and ALOS satellites. The main deformation features seen in the line-of-sight displacement maps indicate subsidence concentrated in the southern and northern parts of the main rupture, in particular at the Indiviso fault, at the Laguna Salada basin, and at the Paso Superior fault. We show that the near-field GPS and InSAR observations over a time period of 5 months after the earthquake can be explained by a combination of afterslip, fault zone contraction, and a possible minor contribution of poroelastic rebound. Far-field data require an additional mechanism, most likely viscoelastic relaxation in the ductile substrate.

Observations and Modeling of Coseismic and Postseismic Deformation Due To the 2015 Mw 7.8 Gorkha (Nepal) Earthquake

“…We assumed that the poroelastic rebound is confined to the top 20 km of the crust and the drained and undrained values of the Poisson's ratio of 0.25 and 0.28, respectively. Similar conclusions were reached in several previous studies of large shallow earthquakes (e.g., Barbot et al, 2008;Gonzalez-Ortega et al, 2014). Figure 12 shows the predicted surface displacements due to the poroelastic rebound.…”

A comparison of long‐term changes in seismicity at The Geysers, Salton Sea, and Coso geothermal fields

“…Regional fault systems also produce large earthquakes that follow more typical main shock‐aftershock sequences, such as the 1987 M 6.6 Superstition Hills [ Hudnut et al , ] and the 2010 M 7.2 El Mayor‐Cucapah [ Wei et al , ] earthquakes. The El Mayor‐Cucapah event ruptured a set of faults within the Cucapah Mountains in Baja California [ Fletcher et al , ; Gonzalez‐Ortega et al , ], but its extensive aftershock sequence extended northward into the Salton Trough [ Hauksson et al , ].…”

Fault geometry inversion and slip distribution of the 2010 Mw 7.2 El Mayor‐Cucapah earthquake from geodetic data

“…Model fitting residuals (black arrows) and the first 6 month postseismic displacement (white arrows; data from Gonzalez‐Ortega et al . []). The colors in the circles represent the model underfitting (blue) or overfitting (red).…”