The Interplay Between Seismic and Aseismic Slip Along the Chaman Fault Illuminated by InSAR

Abstract

AbstractThe 700‐km‐long Chaman fault (CF) marks the western edge of the plate boundary between India and Eurasia. Although global plate models predict 2.3–3.6 cm/yr left‐lateral motion between both plates, the fault is known to have hosted few earthquakes in historical times. Recent geodetic measurements attested the presence of aseismic slip locally. To detail the interplay between fast and slow slip along the CF, we build three Interferometric Synthetic‐Aperture Radar time series of ground deformation covering the whole fault length over 5 years (2014–2019). We find that most of the active fault trace slips aseismically and continuously. From south to north, we identify three creeping fault portions: the Nushki, Central, and Qalat segments of lengths between 80 and 130 km. The loading rate is 1.2 ± 0.3 cm/yr for the two southernmost portions, while it is about 0.7 ± 0.2 cm/yr for the Qalat segment. The Central segment and the nearby locked segments have hosted the largest known historical earthquakes on the CF, and three moderate magnitude earthquakes in our observation period. We image these earthquakes for which modeled slip at depth (Mw5–5.6), time series of surface slip and deformation patterns argue toward large triggered aseismic slip. The June 2018 event displays postseismic moment 3–15 times greater than coseismic moment. Over the two decades covered by geodetic observations, continuous or triggered aseismic slip dominates along most of the fault and co‐locates with earthquakes. We observe that fault geometrical complexities delimit active segments and may be responsible for the kilometer‐scale intertwining between seismic and aseismic events.