Kernel-based 3-D coda (QC−1) mapping of the Eastern part of Kutch Rift Basin, NW India
摘要
The Kutch Rift Basin (KRB), a pericratonic rift basin on the western margin of India, formed during the Late Triassic to Early Jurassic due to the rifting of Eastern Gondwana. It is one of the most seismically active regions that has experienced devastating earthquakes, including 1819 Allah Bund (Mw 7.8), 1956 Anjar (Mw 6.0), and 2001 Bhuj (Mw 7.7) in the last 200 years. Understanding seismic wave attenuation in such a tectonically complex region is critical, as it provides insights into crustal heterogeneities, fluid distribution, and fault zone properties, which are essential for unravelling the seismic hazard potential and tectonic evolution of the region. This study presents a 3D coda wave attenuation (Qc⁻1) model of the central KRB at central frequencies of 1.5 and 3 Hz, derived from 3,404 local earthquake events using a sensitivity kernel approach based on Paasschen’s equation within the framework of radiative transfer theory. Checkerboard tests were conducted to evaluate model stability and resolution and it is observed that optimal results were found in 10–40 km depths. The model reveals moderate to high attenuation anomalies in the upper 15 km, attributed to thick sedimentary deposits and upper crustal heterogeneity. A highly attenuated zone at 20–30 km depth in the eastern region suggests fluid-filled fractures or intrinsic attenuation within fault zones. A narrow moderate attenuation zone at 35–40 km depth in the central part of the study region may indicate a deep fluid reservoir. The Kachchh Mainland Fault (KMF) zone exhibits high attenuation down to 15 km, while the South Wagad Fault (SWF) zone shows moderate to high attenuation extending to 40 km, suggesting SWF serves as a primary conduit for fluid migration from the reservoir to epicentral depths. These findings provide new insights into the crustal structure and fluid dynamics of the KRB, enhancing our understanding of its seismic activity.