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Seismic Site Characterization of Sikkim Himalaya Using HVSR

Description: 

The northeastern state of Sikkim lying in the central segment of the Himalaya orogen is a seismically active region which was plagued by the recent 2011 M_w6.9 earthquake. Analysis of local earthquakes recorded at the recently deployed seismic network of 27 broadband seismic stations revealed multiple seismically active domains with peculiar stress orientations. This makes it imperative to study the site characteristics crucial for determining the local site conditions in the face of prevalent seismic activity. In this study, we compute the horizontal-to-vertical spectral ratio (HVSR) of ambient noise for local site characterization using the resulting peak amplification (A₀) and resonant frequency (f₀). Since our network was operational during the COVID-19 pandemic, we have used the night time data during the lockdown period to ensure analysis of the most stationary part of noise. HVSR curves are observed to be varying distinctly with regional geology. Stations installed over the sedimentary basin exhibit high A₀at low f₀, signifying the underlying thick deposits and sharp impedance contrast. Multiple dipping sheets of the Lesser Himalayan Duplex (LHD) could possibly be responsible for the double amplification peaks observed at stations installed over and around the LHD. The high elevation topography of Higher Himalaya experiences great wind speeds, which has the tendency to induce anomalously high A₀at low f₀evidenced by stations installed in northern Sikkim. We plan to further investigate how the sites respond during earthquakes, and also monitor if the HVSR trends vary temporally.

Session: How Well Can We Predict Broadband Site-Specific Ground Motion and Its Spatial Variability So Far? [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Mita

Student Presenter: Yes

Invited Presentation: 

Authors