Fault Geometry and Slip Distribution of the 2013 Mw 7.7 Balochistan Earthquake From Inversions of SAR and Optical Data

Abstract

The 2013 Mw 7.7 Balochistan earthquake ruptured the Hoshab fault (Pakistan) over 200 km. It was dominated by left‐lateral slip, with a secondary reverse component. By combining optical (SPOT 5 and Landsat 8) and radar satellite data (RADARSAT‐2 and TerraSAR‐X ScanSAR), we derive the 3‐D coseismic displacement field and the slip distribution. Our modeling strategy involves two successive inversions allowing to explore first the fault geometry and then slip distribution. Following a statistical analysis of the coseismic surface trace, the fault is discretized into 16 segments. To determine the dip angle and down‐dip width of the segments, we then perform a non‐linear elastic inversion of the geodetic data set. Using output of this model, we prescribe the fault geometry and linearly invert for slip at depth with refined discretization. Results show a decrease of the fault dip, reaching 50° in the central part of the fault that structurally connects the two sub‐vertical terminations dipping at >70°. The distribution of strike‐slip forms a shallow continuous patch (0–8 km) that peaks at 12.7 m of slip near the epicenter. Reverse slip is distributed on several patches and becomes shallower near the southern termination, where it peaks at 5.7 m. Our model shows an absence of shallow slip deficit (SSD), as for other Mw 7.5 + strike‐slip earthquakes elsewhere, hence suggesting that SSD is only found for lesser magnitude earthquakes. We speculate that moment magnitude is a key element in the occurrence of SSD.

Permanent Co‐Seismic Deformation of the 2013 Mw7.7 Baluchistan, Pakistan Earthquake From High‐Resolution Surface Strain Analysis

“…The September 24, 2013 Mw7.7 Baluchistan earthquake ruptured a ∼200 km segment of the Hoshab fault, a curved reverse fault dipping degree northwest (Avouac et al, 2014;Barnhart et al, 2014;Gold et al, 2015;Zinke et al, 2014). The dip of the fault changes along-strike, which is the lowest (∼50°) in the central part of the fault and increase toward the southern and northern terminuses (>70°, Lauer et al, 2020). The earthquake occurred within the eastern Makran accretionary prism, a region accommodating active subduction of the Arabia oceanic plate beneath continental Eurasia plate to the southwest (DeMets et al, 2010), and left-lateral motion between India and Eurasia plates to the northeast (Lawrence et al, 1981 DeMets et al, 2010).…”

“…The CHENG AND BARNHART 10.1029/2020JB020622 2 of 19 earthquake initiated on a releasing structure near the northern end of the Hoshab fault and propagated bilaterally with average strike-slip of ∼10 m and fault-normal motion of ∼2.5 m (Avouac et al, 2014;Barnhart et al, 2014). Source models show no attenuation of slip magnitude at shallow depths, suggesting no shallow slip deficit (Avouac et al, 2014;Barnhart et al, 2014;Lauer et al, 2020).…”

“…The overall PFZW seem to inversely correlate to fault dip (100-200 m for Baluchistan and Kumamoto, and 25-32 m for Ridgecrest). For the 2013 Baluchistan earthquake alone, Lauer et al (2020) investigated the fault geometry of the Hoshab fault and found varying dip angle along-strike, with increasing angle (>70°) toward the southern and northern terminus and decreasing dip to 50° toward the central part of the fault. The observation of decreased PFZW toward the ends of the rupture (Figure 6) again suggest that the PFZW may inversely correlate to dip angle.…”

Revisiting the 1959 Hebgen Lake Earthquake Using Optical Image Correlation; New Constraints on Near‐Field 3D Ground Displacement

“…OIC has become a standard method for retrieving the surface displacement field created by large strike‐slip earthquakes (e.g., Gold et al., 2021; Lauer et al., 2020; Leprince et al., 2007; Michel et al., 1999; Rosu et al., 2015; Van Puymbroeck et al., 2000; Zinke et al., 2019). To measure co‐seismic displacements OIC compares the pixel shift between pre‐earthquake and post‐earthquake images (Leprince et al., 2007).…”

Mapping and classifying large deformation from digital imagery: application to analogue models of lithosphere deformation

“…Applications range from mapping surface motions [Hampel et al, 2004], to the determination of strain in the horizontal plane [Boutelier and Oncken, 2011] or in side view [Cruz et al, 2008], to the imaging of mantle flow in models [Funiciello et al, 2006]. Similar correlation techniques are employed to detect near step-wise displacements from coseismic deformation using optical satellite imagery [Kääb et al, 2017, Sotiris et al, 2018, SAR data [Morishita et al, 2017] or a combination of both [Lauer et al, 2020].…”