Civil Insight: A Technical Magazine Volume 3 | Page 51

Civil Insight (2019) 51-56 Civil Insight: A Technical Magazine Earthquake Aftershock Removal and Determination of Seismicity Parameters at the Dam Site of Upper Seti Hydropower Project 1,* Pradeep Shrestha, 2 Prachand Man Pradhan, 3 Shiva Prasad Timalsina 1 Student, ME in Structural Engineering, Department of Civil Engineering, Kathmandu University, Nepal, [email protected] 2 Associate Professor, Department of Civil Engineering, Kathmandu University, Nepal, [email protected] 3 Senior Engineer, Insight Engineering Consult Pvt. Ltd., New Baneshwor, Kathmandu, Nepal, [email protected] Abstract This study is focused on analyzing all the available earthquake data, identification, and removal of aftershocks and determination of seismicity parameters at the dam site of Upper Seti Hydropower Project, located at Damauli, Tanahu district, in the western part of Nepal. Initially, earthquake data including epicenters, date of occurrence, and magnitude were collected, following which all the earthquakes were converted into a single magnitude (Moment Magnitude). The converted magnitudes consist of both major events and aftershocks. The aftershocks were then removed . Finally, the Gutenberg-Richter seismicity parameters, ƒ and „ , were determined for the dam site. Keywords: Moment Magnitude, Declustering, Seismicity parameters 1) Introduction Earthquakes are the most unpredictable and uneven natural events. Generally, hazards related to earthquakes are studied under seismic hazard analysis. Earthquake source identification, characterization of seismic source zone, and evaluation of earthquake sizes from those source zones are carried out during hazard analysis. The distribution of earthquake sizes in a given period is described by recurrence law and seismicity parameters. 1.1) Selection of dam-site The dam site of Upper Seti Hydropower Project located at Damauli was selected for the study, which is located in the upper part of the Seti River, a tributary of River Trishuli flowing in the central part of Nepal. The installed capacity of this hydropower project is 127MW and the concrete gravity dam is 140m high. The location of concrete gravity dam is 27°57’ latitude and 84°15’ longitude according to the feasibility study report by Japan International Cooperation Agency (JICA, 2007). The Fig. 1 shows the dam site of Upper Seti Hydropower Project. The main purpose of this study is to collect and analyze past earthquake events in Nepal. The events include both major earthquakes and aftershocks. The aftershock events were removed, referred to as declustering. Gutenberg-Richter recurrence law (1944) was then used to determine the seismicity parameters at the dam site. 2) Methodology 2.1) Earthquake data processing Earthquake data consisting of epicenter, magnitudes, and date of occurrence from 1255 to 2018 AD were *Corresponding Author Email address: [email protected] (Pradeep Shrestha) Submitted on October 8, 2019; Accepted on December 15, 2019 51