Seismic sources, seismotectonics and earthquake recurrence for the KZN coastal regions.

Abstract

Historical earthquake information forms a critical dataset for seismotectonic investigations that can be used for seismic hazard investigations of hazardous and high rise structures and national seismic hazard maps. This study systematically interrogates historical earthquake data for the region from various sources in order to have a better understanding of the origins of the larger earthquakes. Several previously undocumented earthquakes were found that can supplement the national catalogue. Various sources are postulated as origins of these tremors namely local sources located in Mtubatuba and offshore sources like the Mozambique Channel. A seismotectonic model of the study region is also presented from an analysis of earthquake data, structural and kinematic systems. Geo-spatial data from geology, tectonics, regional geophysical anomalies, historical and instrumental seismicity and kinematics are considered. For what was once considered as a diffuse seismotectonic region with low levels of seismicity and where insufficient, uncertain and incomplete data existed – we now have datasets that are more complete and have higher levels of accuracy. Earthquake epicentres from both the historical and instrumental record as well as thermal spring localities correlate with old Jurassic faults. An assembly of a variety of datasets and studies are performed followed by a delineation of respective seismotectonic provinces. Earthquake recurrence parameters were assessed for the seismic provinces. Many of the provinces had insufficient seismic data to compute parameters. Improved seismic monitoring of the east coast region is required to better characterise the seismic risk. These results re-emphasize the need to better understand the coastal environment for seismotectonic characterization and to densify the seismic network towards the eastern coastline.