ISTerre seminar

From the Balochistan earthquake to the creeping segments of the Chaman fault: insights from spatial geodesy

Tuesday 10 March 2020 - 11h00
Benjamin Lauer  - IPGP
--- 
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, Landsat 8) and radar satellite data (RADARSAT-2, TerraSAR-X ScanSAR), we derive the 3D 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 dataset. Using output of this model, we prescribe the fault geometry and linearly invert for slip at depth with refined discretization. Our model shows an absence of shallow slip deficit (SSD), as for other Mw7.5+ 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. Moreover, a few segments of the strike-slip Chaman fault, north of the Balochistan earthquake, are prone to shallow aseismic creep at a rate of around 1cm/yr and may have impeded the Balochistan earthquake rupture propagation northward. To better understand this creeping sections, we aim to enable creep rate measurements from Corona historical images. Both the atypical acquisition procedure of these images (panoramic pushbroom) and the lack of metadata impose a reassessment of part of the photogrammetric processing. More specifically, we first implemented a dedicated camera model and a fully automated method to compute Ground Control Points for Corona images using current SPOT 6/7 imagery, allowing for calibrating the camera model and georeference the historical images.

Organizing team : Cycle sismique et déformations transitoires

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères