Frequency-dependent Layered Q Model and Attenuation Tomography of the Himachal North-West Himalaya, India: Insight to Explore Crustal Variation

Abstract

The three-dimensional attenuation structure and frequency-dependent attenuation layered model are proposed for constraining seismic hazards and exploring the presence of an intra-crustal high conductive (ICHC) layer in the Himachal Himalaya, India. Using acceleration data recorded in the Himachal Himalaya, this work quantifies the attenuation characteristics in the form of shear-wave quality factor (Q_β). The low Q_β values (ranging 10–60) depict an aqueous fluid zone starting from a depth of ~ 11 km. This aqueous fluid identified in the study region closely resembles the ICHC layer identified by other researchers in its adjacent area. The geometry of the Main Himalayan Thrust (MHT) is explored in terms of the obtained attenuation model, which suggests the absence of a ramp structure of MHT below the Main Central Thrust (MCT) in the study region. The presence of an aqueous fluid zone identified at 11–20 km depth may be one of the possible reasons for high seismicity in the Himalayan seismic belt. This work also suggests a frequency-dependent shear wave attenuation (Q_β(f)) model of the form Q_of ⁿ for six different layers of 5 km thickness each. The obtained layered model suggests low Q values, i.e., (49 ± 16) f ^(0.60±0.12) for layer 3 (10–15 km) and (27 ± 11) f ^(0.99±0.18) for layer 4 (15–20 km), corresponding to the aqueous fluid in the study region. The obtained Q_β(f) model appraises the region’s seismic hazard by describing the heterogeneity and tectonic activity level in the present study region.