Improved earthquake location in the gold mining regions of South Africa using new velocity models

Abstract

Reliable local earthquake locations depend on many factors of which a major one is the velocity model. Currently the Council for Geoscience (CGS) has been using the global IASP91 velocity model for earthquake locations in the cluster networks. To continue improving the earthquake locations it is necessary that new velocity models are determined for each cluster region (Central and East Rand - CERAND, the Klerksdorp – Orkney – Stilfontein – Hartebeesfontein – KOSH and the Far West and West Rand - WRAND). The availability of good quality data recorded by the cluster networks since their inception in 2010 provides an opportunity to conduct this work. Thus data from the cluster networks database were selected according to set quality criteria to obtain parametric data for 130 earthquakes in the CERAND region, 404 in the KOSH region and 1024 in the WRAND region. These data were used to determine a minimum 1-D velocity model with associated station corrections for each of the regions using the VELEST software package. Comparison of epicentres obtained using the new velocity models to epicentres previously published by the CGS, showed improvement in the quality of the new locations. Thus, the new models will be implemented in the day-to-day analysis of data recorded in the three study regions by the cluster network of stations.

Hypocenter Determination and Estimation 1-D Velocity Models Using Coupled Velocity-Hypocenter Method

“…The Root Mean Square (RMS error) value in each relocation result is the residual between the observation time (tobs) and the calculation time (tcal) of the hypocenter relocation processing. The preliminary data required to process this method are initial hypocenter data, arrival time recorded on the geophysical station, primary and secondary waves travel time, earthquake station coordinates, and initial velocity model [6].…”

“…1. The relocation of earthquake hypocenter using Couple Velocity-Hypocenter method is a simultaneous relocation of earthquake hypocenter using travel time data [6], where the travel time data was obtained from local earthquake data derived from the Agency for Meteorology, Climatology, and Geophysics of Indonesia (BMKG) catalog. The data were selected to determine the arrival time of the primary waves.…”

“…This research aims to find out the location of the earthquake hypocenter accurately and estimate a one-dimensional Primary wave velocity model that is suitable for determining the high-precision hypocenter location on the Central Sulawesi region. Therefore, this research used Coupled Velocity-Hypocenter Method, which is the relocation of the earthquake hypocenter method, which also produces a new velocity model and station correction simultaneously using the principle of the Geiger method, where the velocity model is updated using the Kissling equation [4]- [6].…”

Identification of Micro-Earthquake Hypocenters using Geiger and Coupled Velocity-Hypocenters Methods

“…The Geiger method is an inversion method that uses P and S waves arrival time data. This method's input parameters include recording station data or seismic station coordinates (codes, coordinates and station elevation value), 1-D of P waves velocity model, P and S waves arrival times data for each micro-earthquake event [3].…”

“…In this method, the velocity model is tested by applying the Kissling equation [7]. Unmodeled hypocenter wave velocity structures can be overcome by location test and modelling of 1-D P wave velocity using the Coupled Velocity-Hypocenters method through the Kissling equation [1]- [3], [8], [9]. The location test results using Coupled Velocity-Hypocenters method obtained a new 1-D velocity model with different vp/vs in each layer [7].…”