Crust and upper mantle velocity structure of the northwestern Indian Peninsular Shield from inter-station phase velocities of Rayleigh and Love waves

We measure the inter-station Rayleigh and Love wave phase velocities across the northwestern Indian Peninsular shield (NW-IP) through cross-correlation and invert these velocities to evaluate the underneath crust and upper mantle velocity structure down to 400 km. We consider a cluster of three stations in the northern tip of the Peninsula and another cluster of eight stations in the south. We measure phase velocities along 28 paths for Rayleigh waves and 17 paths for Love waves joining two stations with one from each cluster and using broadband records of earthquakes which lie nearly on the great circle joining the pair of stations. The phase velocities are in the period range of 10 to 275 s for Rayleigh waves and of 10 to 120 s for Love waves. The isotropic model obtained through inversion of the phase velocities indicates 199.1 km thick lithosphere with 3-layered crust of thickness 36.3 km; the top two layers have nearly same velocities and both constitute the upper crust with thickness of 12.6 km. The upper crust is mafic, whereas the lower crust is felsic. In the mantle lid, velocities increase with depth. The velocities of mantle lid beneath NW-IP is lower than those beneath south Indian Peninsula showing the former is hotter than the later perhaps due to large Phanerozoic impact on NW-IP. The significant upper mantle low velocity zone beneath NW-IP indicates high temperature which could be attributed to the past existence of a broad plume head at the west-central part of the Peninsula

Crustal velocity structure of the Deccan Volcanic Province, Indian Peninsula, from observed surface wave dispersion

Through inversion of fundamental mode group velocities of Love and Rayleigh waves, we study the crustal and subcrustal structure across the central Deccan Volcanic Province (DVP), which is one of the world’s largest terrestrial flood basalts. Our analysis is based on broadband seismograms recorded at seismological station Bhopal (BHPL) in the central India from earthquakes located near west coast of India, with an average epicentral distance about 768 km. The recording station and epicentral zone are situated respectively on the northern and southern edges of DVP with wave paths across central DVP. The period of group velocity data ranges from 5 to 60 s for Rayleigh waves and 5 to 45 s for Love waves. Using the genetic algorithm, the observed data have been inverted to obtain the crust and subcrustal velocity structure along the wavepaths. Using this procedure, a similar velocity structure was also obtained earlier for the northwestern DVP, which is in the west of the present study region. Comparison of results show that the crustal thickness decreases westward from central DVP (39.6 km) to northwestern DVP (37.8 km) along with the decrease of thickness of upper crust; while the thickness of lower crust remains nearly same. From east to west S-wave velocity in the upper crust decreases by 2 to 3 per cent, while P-wave velocity in the whole crust and subcrust decreases by 3 to 6 per cent. The P- and S-wave velocities are positively correlated with crustal thickness and negatively correlated with earth’s heat flow. It appears that the elevated crustal and subcrustal temperature in the western side is the main factor for low velocities on this side.</p

Estimating tsunami potential of earthquakes in the Sumatra-Andaman region based on broadband seismograms in India

Estimating tsunami potential of earthquakes in the Sumatra–Andaman region based on broadband seismograms in IndiaIn this paper, we report that the ratio of broadband energy (0.01–2 Hz) to highfrequency energy (0.3–2 Hz), Er, estimated from regional seismograms of India, might be a useful parameter in estimating tsunami potential of earthquakes in the Sumatra–Andaman region. Er is expected to be sensitive to the depth as well as to the source characteristics of an earthquake. Since a shallow and slow earthquake has a greater tsunamigenic potential, Er may be a useful diagnostic parameter. We base our analysis on broadband seismograms of the great earthquakes of Sumatra–Andaman (2004, Mw * 9.2) and Nias (2005, Mw 8.6), 41 of their aftershocks, and the earthquakes of north Sumatra (2010, Mw 7.8) and Nicobar (2010, Mw 7.4) recorded at VISK, a station located on the east coast of India. In the analysis, we also included the two recent, great strike-slip earthquakes of north Sumatra (2012, Mw 8.6, 8.2) recorded at VISK and three south Sumatra earthquakes (2007, Mw 8.5; 2007, Mw 7.9; 2010, Mw 7.8) recorded at PALK, a station in Sri Lanka. We find that Er is a function of depth; shallower earthquakes have higher Er values than the deeper ones. Thus, Er may be indicative of tsunamigenic potential of an earthquake. As Mw and Er increase so does the tsunami potential. In addition to the parameter Er, the radiated seismic energy, Es, may be estimated from the regional seismograms in India using empirical Green’s function technique. The technique yields reliable Es for the great Sumatra and Nias earthquakes. Er and Es computed from VISK data, along with Mw and focal mechanism, may be useful in estimating tsunami potential along the east coast of India from earthquakes in the Sumatra–Andaman region in less than 20 min.En este trabajo, informamos de que la relación entre la energía de banda ancha (0,01-2 Hz) y la energía de alta frecuencia (0,3-2 Hz), Er, estimada a partir de sismogramas regionales de la India, podría ser un parámetro útil para estimar el potencial de tsunami de los terremotos en la región de Sumatra-Andamán. región de Sumatra-Andamán. Se espera que Er sea sensible a la profundidad así como a las características de la fuente de de un terremoto. Dado que un terremoto poco profundo y lento tiene un mayor potencial tsunamigénico, Er puede ser un parámetro de diagnóstico útil. Basamos nuestro análisis en sismogramas de banda ancha de los grandes terremotos de Sumatra-Andaman (2004, Mw 9,2) y Nias (2005, Mw 8,6), 41 de sus réplicas, y los terremotos del norte de Sumatra (2010, Mw 7,8) y Nicobar (2010, Mw 7,4) registrados en VISK, una estación situada en la costa oriental de la India. En el análisis, también se incluyeron los dos grandes terremotos recientes de deslizamiento del norte de Sumatra (2012, Mw 8,6, 8,2) registrados en VISK y tres terremotos del sur de Sumatra (2007, Mw 8,5; 2007, Mw 7,9; 2010, Mw 7,8) registrados en PALK, una estación de Sri Lanka. Encontramos que Er es una función función de la profundidad; los terremotos menos profundos tienen valores de Er más altos que los más profundos. Por lo tanto, Er puede ser un indicador del potencial tsunamigénico de un terremoto. A medida que la Mw y la Er aumentan también lo hace el potencial de tsunami. Además del parámetro Er, la energía sísmica radiada, Es, puede estimarse a partir de los sismogramas regionales de la India utilizando la técnica de la función de Green empírica empírica de Green. Esta técnica permite obtener Es fiables para los grandes terremotos de Sumatra y Nias. Er y Es calculados a partir de los datos de VISK, junto con Mw y el mecanismo focal, pueden ser útiles para estimar el potencial de tsunami a lo largo de la costa oriental de la India a partir de los terremotos de la región de Sumatra-Andamán en menos de 20 minutos.Universidad Nacional, Costa Rica.Universidad Nacional Autónoma de México, DF, México.India Meteorological Department, India.Observatorio Vulcanológico y Sismológico de Costa Ric

Source characteristics of the 18 September 2011 Sikkim earthquake and zoning

Using detailed waveform analysis of Pn, sPn depth phases from the nearby seismic stations, attempts were made to resolve the focal depth of the 2011 Sikkim earthquake. Focal depth of 46.8 km thus determined was found closer to the GCMT source mechanism solution as compared to ISC solution (29.6 km). Re-examination of its source mechanism with the spatial/ depth distribution of its aftershocks sug- gested that both the nodal planes oriented WNW or ENE, initially ruptured but the orientation of meizoseismal area and larger concen- tration of its aftershocks parallel to the Tista lineament conformed WNW striking nodal plane relatively more active. The large value of the stress drop derived from S-wave spectra based on the data of Indian stations was attributed to its strike-slip mechanism and deeper focal depth. The stress drop of its foreshock was much lower than that the main shock. The b-value also showed a decrease during the last decade prior to the main earthquake.The recent Sikkim earthquake (Mw 6.9) has brought out the limitations of the microzoning of the Sikkim region attempted earlier