High Crustal Seismic Attenuation in Ladakh-Karakoram

An analysis of the Lg wave has been attempted in order to study the seismic attenuation Q 0 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 Q 0 measurements using a differential evolution global optimization scheme. The Q 0 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 Q 0 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 Q 0 (∼70). The high attenuation zone (low Q 0 ) 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.