Current Science

B. Naresh ¹, P. Solomon Raju ¹, G. Suresh ¹, A. N. S. Sarma ¹, R. Vijaya Ragavan ¹, Satish Saha ¹, D. Srinagesh ¹

Affiliations
1 CSIR-National Geophysical Research Institute, Hyderabad 500 007, IN

Abstract

The Nellore district in the Southeastern part of Andhra Pradesh is one of the nine coastal districts of the state. The microtremor activity in the district started in October 2015 and continued up to July 2016. During this period, a few hundred tremors were recorded by the temporary seismic network installed locally by the CSIR-NGRI. Apart from the data recorded by this network, those from the semipermanent seismic stations at Racherla, Addanki, Cuddapah, Srikalahasti and Srisailam were used in the study¹.

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D. Srinagesh ¹, Prantik Mandal ¹, R. Vijaya Raghavan ¹, Sandeep Gupta ¹, G. Suresh ¹, D. Srinivas ¹, Satish Saha ¹, M. Sekhar ¹, K. Sivaram ¹, Sudesh Kumar ¹, P. Solomon Raju ¹, A. N. S. Sarma ¹, Y. V. V. S. B. Murthy ¹, N. K. Borah ¹, B. Naresh ¹, B. N. V. Prasad ¹, V. M. Tiwari ¹

Affiliations
1 CSIR-National Geophysical Research Institute, Hyderabad 500 007, IN

Abstract

According to the Gutenberg–Richter law¹, at least one earthquake of magnitude greater than 7 occurs every month along the seismically active belts in the world. Earthquakes are the manifestation of fault slip at depths, thus, there is no direct method to measure or observe them. However, seismometers can record ground velocity or acceleration caused by the occurrence of an earthquake when a fault slip occurs at depth. Therefore, setting up a seismic network is inevitable to understand the physics of earthquake processes, thereby, mitigating earthquake hazard.

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D. Srinagesh ¹, Dhiraj Kumar Singh ¹, G. Vikas ¹, B. Naresh ¹, Sunil Roy ¹, Y. V. V. B. S. N. Murthy ¹, P. Solomon Raju ¹, G. Suresh ¹, Prantik Mandal ¹, A. N. S. Sharma ¹, M. Shekar ¹, V. M. Tiwari ¹

Affiliations
1 CSIR-National Geophysical Research Institute, Hyderabad 500 007, IN

Abstract

The present study focuses on the recent earthquake activity in Palghar region, Maharashtra, India. Until 31 August 2019, a total of 4854 earthquakes have been located here, whose local magnitude (M_L) varied from 0.1 to 4.1. Majority of the earthquakes (~94%) were located in the depth range 4–16 km. The precise earthquake relocations reveal two clusters. The N–S trending cluster north of 20.04°N extends to a depth of 10 km, whereas the NE–SW trending cluster to the south of 20.04°N extends to 16 km depth. The shallow northern cluster is noticed to be sandwiched between two mapped mafic intrusions, whereas the deeper southern segment shows earthquakes clustering around the mafic intrusion. The modelled composite focal mechanism solutions for both the north and south clusters suggest normal faulting with a minor strike–slip component as the dominant deformation mode for the Palghar region. From relocated seismici-ty, we have detected a deeper seismically active zone (with M> 3) at 4–16 km depth, occupying a crustal volume of 1440 km 3 (i.e. 20 km (in N–S) ×6 km (in E– W) and 12 km (in depth)) that dips toward 20°S and 70°W. This could be attributed to the large crustal stresses induced by the mafic intrusive body below the region.

Keywords

Crustal Stress, Deformation Mode, Earth-quake, Mafic Intrusion, Relocations, Seismic Activity.

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R. Pradeep Kumar ¹, D. Srinagesh ², T. Seshunarayana ², R. K. Chadha ², Narender Bodige ³, G. Suresh ², D. Hima Chandan ¹, C. V. R. Murty ⁴

Affiliations
1 Earthquake Engineering Research Centre, International Institute of Information Technology, Hyderabad 500 032, IN
2 CSIR-National Geophysical Research Institute, Hyderabad 500 007, IN
3 Department of Civil Engineering, Anurag Group of Institutions, Hyderabad 501 301, IN
4 Department of Civil Engineering, Indian Institute of Technology Madras, Chennai 600 036, IN

Abstract

A ground-structure vibration response study was carried out at the Ramappa Temple near Warangal, Telangana, India, shaken by underground blasting undertaken at the neighbouring Devadula Lift Irrigation Project to build water tunnels. The intensities of vibrations were examined – subsurface and ground vibrations were measured using velocity meters, and shaking at the temple using accelerometers. The study concluded that high-frequency vibrations of the ground were filtered by the soft natural clay bed underneath, and vibrations at the temple structure were small and well below the levels that can cause damage to it. Here we present the scientific findings of the vibrations recorded during the blasts and their implications.

Keywords

Heritage Structure, Structural Response, Tunnel Blasting, Vibrations, Vulnerability Assessment.

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