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Seismic landslide hazard assessment of central seismic gap region of Himalaya for a Mw 8.5 scenario event

Nayek Partha Sarathi, Gade Maheshreddy

Acta Geophysica

2021

Vol. 69, no. 3

747--759

In this study, seismic landslide hazard analysis is performed for central seismic gap (CSG) region of Himalaya for a future scenario earthquake of magnitude (Mw) 8.5. Initially, PGA values are estimated by using stochastic fnite fault seismological model. Further, the PGA values along with slope displacement prediction equation are used to estimate the Newmark’s sliding displacement. Monte Carlo simulations are performed by considering uncertainties in the material properties. Finally, the hazard map in terms of the probability of slope displacement (DN) value exceeding the threshold values of 5 cm is presented. The probability value varies between 0.1 and 1 and high probability in higher Himalayas highlights the possibility of huge number of co-seismic landslides in this region. The developed seismic landslide hazard map will help local authorities and planners with tools for assessing the seismic landslide risk associated with the use of land and taking necessary measures to minimize the damages.

Testing the performance of earthquake early warning system in northern India

Mittal Himanshu, Wu Yih‑Min, Sharma Mukat Lal, Ming Yang Benjamin, Gupta Sushil

Acta Geophysica

2019

Vol. 67, no. 1

59--75

The main goal of present study is to test the functionality of an earthquake early warning (EEW) system (a life-saving tool), in India using synthesized data and recorded earthquake data from Taiwan. In recent time, India set up an EEW system in the central seismic gap along the Himalayan Belt, consisting of about 100 low-cost P-Alert instruments. The area, where these instruments are installed, is highly sensitive to the seismic risk with the potential of strong, major and great earthquakes. In the absence of recorded data from the Himalayas required for analysis of such system, we take advantage of recorded waveforms from Taiwan, to test the EEW system. We selected Taiwanese stations in good accordance with the Indian sensor network, to have a best fit in terms of inter station spacing. Finally, the recorded waveforms are passed through Earthworm software using tankplayer module. The system performs very well in terms of earthquake detection, P-wave picking, earthquake magnitude and location (using previously estimated regressions). Pd algorithm has been tested where the peak amplitude of vertical displacement is used for estimating magnitudes using previously regressed empirical relationship data. For the earthquakes located between Main Boundary Thrust and Main Central Thrust along with a matching instrumentation window, a good estimate of location, as well as magnitude is observed. The approach based on Pd for estimating magnitude works perfectly as compared to _ c approach, which is more sensitive to signal-to-noise ratio. To make it more region specific, we generated synthetic seismograms from the epicenters of historical Chamoli (1999) and Uttarkashi (1991) earthquakes at EEW stations in India and checked the functionality of EEW. While placing these earthquakes within the instrumentation window, a good approximation of earthquake location and magnitude is obtained by passing these generated waveforms. The parameters used to judge the performance of EEW system included the time taken by the system in issuing warning after the confirmation of the occurrence of damaging earthquake and the lead time (time interval between the issuing of warning and arrival of damaging earthquake ground motion at a particular location). High lead times have been obtained for the plainer regions including thickly populated regions of Gangetic plains, such as Delhi National Capital Region according to the distance from the epicenter, which are the main target of EEW system.