A silent Mw 4.7 slip event of October 2006 on the Superstition Hills fault, southern California

Abstract

During October 2006, the 20‐km‐long Superstition Hills fault (SHF) in the Salton Trough, southern California, slipped aseismically, producing a maximum offset of 27 mm, as recorded by a creepmeter. We investigate this creep event as well as the spatial and temporal variations in slip history since 1992 using ERS‐1/2 and Envisat satellite data. During a 15‐year period, steady creep is punctuated by at least three events. The first two events were dynamically triggered by the 1992 Landers and 1999 Hector Mine earthquakes. In contrast, there is no obvious triggering mechanism for the October 2006 event. Field measurements of fault offset after the 1999 and 2006 events are in good agreement with the interferometric synthetic aperture radar data indicating that creep occurred along the 20‐km‐long fault above 4 km depth, with most of the slip occurring at the surface. The moment released during this event is equivalent to a Mw 4.7 earthquake. This event produced no detectable aftershocks and was not recorded by the continuous GPS stations that were 9 km away. Modeling of the long‐term creep from 1992 to 2007 creep using stacked ERS‐1/2 interferograms also shows a maximum creep depth of 2–4 km, with slip tapering with depth. Considering that the sediment thickness varies between 3 km and 5 km along the SHF, our results are consistent with previous studies suggesting that shallow creep is controlled by sediment depth, perhaps due to high pore pressures in the unconsolidated sediments.