Spatial variations in fault friction related to lithology from rupture and afterslip of the 2014 South Napa, California, earthquake

Abstract

Following earthquakes, faults are often observed to continue slipping aseismically. It has been proposed that this afterslip occurs on parts of the fault with rate‐strengthening friction that are stressed by the main shock, but our understanding has been limited by a lack of immediate, high‐resolution observations. Here we show that the behavior of afterslip following the 2014 South Napa earthquake in California varied over distances of only a few kilometers. This variability cannot be explained by coseismic stress changes alone. We present daily positions from continuous and survey GPS sites that we remeasured within 12 h of the main shock and surface displacements from the new Sentinel‐1 radar mission. This unique geodetic data set constrains the distribution and evolution of coseismic and postseismic fault slip with exceptional resolution in space and time. We suggest that the observed heterogeneity in behavior is caused by lithological controls on the frictional properties of the fault plane.

Buried shallow fault slip from the South Napa earthquake revealed by near-field geodesy

“…4) ( 38 , 41 , 45 ). The hand measurements made at the day of the event ( 34 , 44 ) document a peak in coseismic surface offset in the northern portion of the rupture and a deficit in the south (Fig.…”

Long‐Term Afterslip of the 2004M 6.0 Parkfield, California, Earthquake—Implications for Forecasting Amount and Duration of Afterslip on Other Major Creeping Faults

“…At three South Napa afterslip sites, the rupture propagated upward through 0-3-km-thick basin deposits (Brooks et al, 2015;Floyd et al, 2016); whereas only at the NLOD site was the rupture in bedrock near the surface. However, on the creeping Superstition Hills fault (Wei et al, 2009) after the 1987 M 6.6 earthquake, at the mostly ∼2-3-km-deep basin sites (Williams and Magistrale, 1989), AFTER solutions indicated that most significant afterslip (∼95%) would occur within only 2 yrs .…”

Widespread Fault Creep in the Northern San Francisco Bay Area Revealed by Multistation Cluster Detection of Repeating Earthquakes

“…The former, composed of three repeating events (in 1995, 2000, and 2005), is located on the Browns Valley segment of the fault, ∼ 4 km NW of the northern end of the 2014 earthquake rupture zone (e.g., Floyd et al, 2016) and at 6-km depth. The former, composed of three repeating events (in 1995, 2000, and 2005), is located on the Browns Valley segment of the fault, ∼ 4 km NW of the northern end of the 2014 earthquake rupture zone (e.g., Floyd et al, 2016) and at 6-km depth.…”