Piecemeal Rupture of the Mentawai Patch, Sumatra: The 2008 M_w 7.2 North Pagai Earthquake Sequence

Abstract

The 25 February 2008 Mw 7.2 North Pagai earthquake partially ruptured the middle section of the Mentawai patch of the Sunda megathrust, offshore Sumatra. The patch has been forecast to generate a great earthquake in the next few decades. However, in the current cycle the patch has so far broken in a sequence of partial ruptures, one of which was the 2008 event, illustrating the potential of the patch to generate a spectrum of earthquake sizes. We estimate the coseismic slip distribution of the 2008 event by jointly inverting coseismic offsets from GPS and interferometric synthetic aperture radar. We then estimate afterslip with 5.6 years of cumulative GPS displacements. Our results suggest that the estimated afterslip partially overlaps the coseismic rupture. The overlap of coseismic rupture and afterslip can be explained conceptually by a simple rate‐and‐state model where the degree of overlapping is controlled by the dynamic weakening and the critical nucleation size in the velocity‐weakening area. Comparing our rate‐and‐state model results with our geodetic inversion results, we suggest that the part of the coseismic rupture that does not overlap with the afterslip may represent a velocity‐weakening region, while the overlapping part may represent a velocity‐strengthening region.

Orthogonal Fault Rupture and Rapid Postseismic Deformation Following 2019 Ridgecrest, California, Earthquake Sequence Revealed From Geodetic Observations

“…From the comparison between the aftershocks and geodetic slip models of the 2019 Ridgecrest earthquakes, we can infer that the coseismic ruptures of the Mw6.4 and Mw7.1 events were able to overcome isolated velocity-strengthening patches that now continued to slip during the postseismic process. This is consistent with observed spatial overlap between coseismic and postseismic slips through postseismic studies following several large earthquakes (e.g., Qiu et al, 2019;Salman et al, 2017).…”

Joint Inversion of Coseismic and Early Postseismic Slip to Optimize the Information Content in Geodetic Data: Application to the 2009 Mw6.3 L'Aquila Earthquake, Central Italy

“…The associated surface deformation signals are usually hard to detect and are neglected in coseismic studies. The postseismic deformation happening in the first few days after the mainshock is usually detectable in the geodetic data but incorporated in source estimation problems as if it was part of the coseismic signal (e.g., Barnhart et al., ; Bletery et al., ; Cheloni et al., ; Elliott et al., ; He et al., ; Lin et al., ; Salman et al., ), with the justification that it is comparatively small. Similarly, postseismic models generally do not account for observations related to the early postseismic deformation because they are often contaminated by coseismic signal (e.g., Cheloni et al., ; D'Agostino et al., ).…”

Revised earthquake sources along Manila Trench for tsunami hazard assessment in the South China Sea

“…We cutoff slip deeper than km as the rock properties at this depth and beyond behave semi-brittle and ductile flow (Hippchen and Hyndman, 2008;Hyndman and Wang, 1993;Wang, 2007). By doing so it could capture the first-order of potential slip extent (Figure 3c and f), similar as the estimated depth-range of slip observed from global megathrust great earthquakes (e.g., Chlieh et al 2007;Pollitz et al 2011;Ruiz et al 2014;Salman et al 2017;Wei et al 2012).…”

“…We've seen partial ruptures of fully locked megathrusts (Konca et al, 2008;Qiu et al, 2016;Ruiz et al, 2014;Schurr et al, 2014), and piecemeal breaks in the center of perceived seismic gaps (e.g. Salman et al, 2017). Even with improved observations, it remains difficult to constrain the magnitude of potential earthquake in the first order, and even more difficult to define the rupture pattern (e.g., Lay, 2018 Notably, the rupture models constrained by multiple geodetic data sets after the 2011 earthquake (Koketsu et al, 2011;Meade, 2011, Wei et al, 2012) are significantly different to the coupling map of Loveless and Meade (2010).…”