Seismicity of region around dams in North West India

The collision of Indian and Eurasian continents caused large scale deformation and high seismicityof vast areas of both continents in the geological history. The North-West portion of the Himalayan arc which is lyingunder the rupture zones of Kangra earthquake of 1905, Uttarkashi earthquake of 1991 and Chamoli earthquake in 1999,has experienced many earthquakes of magnitude 6 and above. The region of North-West India between 30.0º - 35.0ºNorth and 73.0º - 79.0º East is, therefore, under intense investigations by various scientists since the origin of theHimalayas. India Meteorological Department had opened thirteen seismic observatories in early sixties for monitoringof earthquake activities in and around Bhakra, Pong, Pandoh dams in Punjab / Himachal Pradesh and Salal dam inJ&K on specific demand of the dam authorities. These observatories have recorded the earthquakes occurred in thisregion having magnitude even less than 2. The data collected for the last two decades is very useful for the scientiststo investigate seismicity and tectonics of the Himalayas. The present study could locate the regions which areseismically most active and also the region of seismic gap. Thus present study confirms association of seismic activityin the region with two major fault systems called Main Boundary Thrust (MBT) and Main Central Thrust (MCT).Comparative seismic activity within 100 km from each dam, reveal that most active region was around Pong followed byPandoh, Bhakra and Salal dams. The temporal variation of b-values for the whole period also shows that low b-valueanomalies are usually followed by large earthquakes of M > 5.5. No definite conclusions could be drawn with regard tothe relationship between the observed seismic activity around the dam sites with the corresponding water levelfluctuations in the reservoirs.

Seismicity Detection in Skopje Region Using Tomographic Methods and 3-D Modelling

<p>A novel geotomography technique has been applied at the epicentral area around capitol of Macedonia - Skopje, using selected earthquakes that occurred over a period of 57 years and were recorded on temporary and permanent seismograph stations. This study will test the tomography method for the first time in investigation of the crustal shape and structures in our tectonic environment using specially designed datasets covering 1964-1967 and 2016-2020 periods.</p><p>In the initial phase, the analysis will show the potential of the geotomography application in revealing detailed velocity perturbation in the lithosphere. Then, the events are relocated in the 3-D models and new cross-sections of the crust produced by a simultaneous approach. The images can help in constraining the velocity vs depth relationship and thus can contribute towards redefinition of the earthquake zones. The results are discussed in terms of general stress and seismic regime and their temporal changes.</p><p>Better understanding of the seismicity and tectonics processes in the Skopje region will lead to an overall improvement of the earthquake hazard assessment at local and national level, as well as further integration in research programs with other geophysical methods.</p><p> </p>

Seismic Tomography of Macedonia

<p>A novel geotomography technique has been applied in and around Macedonia using selected earthquakes that occurred over a period of 40 years and were recorded on 47 seismograph stations. The aim was to test this new tomography method for the first time in investigation of the crustal shape and structures in that specific tectonic environment with an extensive dataset.</p><p>A three-dimensional velocity model and many cross-sections of the crust were produced by this methodology and compared with the previous models of Macedonia. They show the potential of the tomography application in revealing geological features on local and regional scale. </p><p>The new images will contribute towards a better understanding of the seismicity and tectonics in that part of the Balkans and assist in the process of integrated seismic hazard assessment.</p><p> </p><p> </p><p>Keywords: Geotomography, Earthquakes, Seismic Imaging</p>