Coseismic Deformation of the Indonesian Geospatial Reference System 2013 from the 2022 Cianjur Earthquake

Abstract

Indonesia is a country with high seismic activity. Since 2013, Indonesia has used a semi-dynamic geodetic datum, also known as a reference system. Earthquake events can cause surface deformation and alter the coordinates of the Indonesian Geospatial Reference System 2013 (SRGI 2013) points. Changes in these coordinates will affect the computation of new coordinates referenced to SRGI 2013. On November 21, 2022, an earthquake struck the Cianjur area of Indonesia. This study aims to calculate the displacement of SRGI 2013 points around the epicenter of the Cianjur Earthquake due to coseismic deformation using continuous GNSS observation data and to analyze the effect of this deformation on the SRGI 2013 reference frame. The earthquake caused significant horizontal displacement at STA CJUR and significant vertical displacement at five GNSS CORS SRGI 2013 stations. The horizontal displacement of the GNSS CORS stations ranges from 0.001 m to 0.0445 m (1 mm to 44.5 mm). The vertical displacement ranges from −0.0038 m to 0.0125 m (−3.8 mm to 12.5 mm). The largest horizontal and vertical displacements occurred at CJUR Station, which is the closest station to the epicenter. Although the horizontal deformation at STA CJUR only affects the 1:100 class 1 base map scale, it also affects control point measurement activities for mapping at a scale of 1:1,000 or smaller. Therefore, redefining the STA coordinates using new epochs or incorporating earthquake-induced deformation information into the deformation model is recommended. The densification of control points in Indonesia's SRGI reference framework will henceforth take into account locations near earthquake sources in order to support more accurate calculation of earthquake-induced deformation models. A more accurate deformation model can improve the quality of SRGI as a semi-dynamic datum.