Spatiotemporal Variations Of B-value And Their Relationship With Fault Blocks In Western Tibet

Tibet is considered as the youngest orogenic belt resulted from the collision of the Eurasian plate and Indian plate.Now-a-days major focus is on its crust-mantle structure study in earth sciences,and western Tibet is a massive and important area for the research.The bvalue of seismic activity becomes an important information window to reveal the regional crust-mantle structure.The plateau encounters compression in the south due to Indian plate subducting beneath the Eurasian plate.In Tibetan plateau high seismicity,distinct geological structures and spatial heterogeneity make it one of the best natural laboratories for seismological researches.In this study,we have covered the whole western part of the Tibet plateau extending from north to south.The study area lies at 27°N–36.5°N,78°E–89°E in western Tibet is enormous and a lot of deformation has occurred in the region,so the whole area was divided into fault blocks.The Tibet plateau,along with the fault blocks in the plateau,is moving towards the southeastward direction,and faults in the faults blocks region have different slip rates.The plateau mostly consists of strike-slip faults along with the normal and thrust faults.The present study is conducted to determine spatiotemporal variations of b-value in the western Tibet plateau and its relation with the fault blocks in the region.A catalog recorded from 2009–2019 consisting of 4432 well-located earthquakes were used to analyze the b-value in the study area.The data was obtained from the China seismological network ranging in magnitude from 0.1M to 8.2M.The study area consists of 4 significant earthquakes events,with magnitudes greater than 7,which occurred between 2014 and 2015.The maximum depth of the earthquakes in the region is 256 km,whereas;depth histogram shows that most of the earthquakes are shallow earthquakes,and the b-value is decreasing with increasing depth.As the b-value decreases,we encounter the large magnitude earthquakes.Time histogram shows us that the earthquakes occurred in the period ranging from 2009 to 2019.However,most of the earthquakes happened in the year 2014–2015.The b-value computed in the study area is 0.3 to 1.4.Most of the study area has the b-value 0.4 to 0.8,which is a low/intermediate value due to the presence of strike-slip faults and under-thrusting in the region.High b-value is found in the NW and East of the area,which shows us that the domain is prone to small earthquakes in the near future.We can also see a decrease in the b-value before the massive earthquake with magnitude 8.2,which occurred in the study area in 2015.Low b-value shows us a small degree of variation in rock properties,which are of great stress and strain,fractured medium,high deformation speed,and significant faults.The recent trend of the b-value shows us that the value is in the phase of decreasing and accumulations of stress are happening,which might cause a massive earthquake in the near future.To further strengthen the seismic hazard study,it will be necessary to have more seismic station coverage in the area so that more data can be acquired and interpreted.Field data should be obtained to study the significant faults in the active tectonic area,which is difficult due to the rough terrain and harsh environment.To strengthen the seismicity analysis and study in the plateau,concentration should be to study the whole seismicity pattern,the seismicity level,its migration,and endeavor to catch foreshocks after a main shock.Mass prediction and disaster prevention of earthquakes,uniform arrangement,and combined observation should be promoted to gain deeper insights into the changes of the precursory field and improve the short-term and imminent earthquake prediction.Based on the intensive view in the plateau,keep an observant eye on probable migration of the central seismic active region to other places to prepare against the unexpected events and the associated sudden disasters.