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High Crustal Seismic Attenuation in Ladakh–Karakoram

National Geophysical Research Institute, Uppal Road, Hyderabad-500007, India

Amit Padhi

Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur-721302, India

P. Rajgopala Sarma

National Geophysical Research Institute, Uppal Road, Hyderabad-500007, India

An analysis of the Lg wave has been attempted in order to study the seismic attenuation Q₀ along a profile from the southern edge of the northwestern Himalaya to Ladakh and Karakoram using broadband waveform recordings of regional earthquakes. The lateral variability in seismic attenuation is derived from the inversion of 23 two-station Q₀ measurements using a differential evolution global optimization scheme. The Q₀ value decreases northwards from 700 in Himalaya and 400 beneath the Indus Zangbo suture (IZS) to 70 in Ladakh–Karakoram. This suggests an efficient transmission of seismic waves beneath the Himalaya and the IZS and high attenuation under Ladakh–Karakoram. The Q₀ values for northwestern Himalaya and the IZS are significantly (>50%) higher compared to their counterpart at 90° E, while Ladakh–Karakoram and southern Tibet show comparable Q₀ (70). The high attenuation zone (low Q₀) is correlatable with increase in electrical conductivity and decrease in the midcrustal S velocity, suggesting the possible presence of aqueous fluid/partial melt in the Ladakh crust.