Publication Date:
2023-07-18
Description:
Using data from a 60-station network in Kumaon-Garhwal (2017-2022), we discovered a north dipping (2o) low-velocity zone (10-20% drop in Vp and Vs, 10-15% increase in Vp/Vs) between 10 and 20 km depths that correlated with the main Himalayan thrust (MHT). It is worth noting that the rupture zones of the 1803 Mw7.6 Garhwal, 1991 Mw6.8 Uttarkashi, and 1999 Mw6.5 Chamoli earthquakes are all characterised by low-velocity zones, implying that the earthquakes were triggered by the presence of metamorphic or aqueous fluids within the MHT. Through the Common Conversion Point stacking of radial PRFs, we also detect a double Moho structure beneath the aforementioned rupture zones, which could be accumulating high crustal stresses favouring the moderate to large earthquake occurrences in the region. Our H-K stacking of radial PRFs, as well as joint inversion of radial PRFs and Rayleigh wave group velocity dispersion, resulted in three NNE-SSW trending transverse crustal blocks with significant mafic crust thinning, which are projected to extend down to the lithosphere-asthenosphere boundary. These three transverse lithospheric characteristics correlate to the northward extension of the Delhi-Haridwar ridge, a presumed tectonic boundary (marked by the intersection zone of rupture zones associated with the 1505 Mw8.2 and 1803 Mw7.6 earthquakes), and the Great Boundary fault, in that order. As a result, we hypothesise that these transverse structures may have segmented the lithosphere (below the MHT) in the Uttarakhand Himalaya, reducing the potential rupture lengths and, as a result, the probability of future large earthquakes (M≥8) in the region.
Language:
English
Type:
info:eu-repo/semantics/conferenceObject
Permalink
