High-Precision Hypocentre Determination for Local Earthquakes

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The last decade has seen a revolution in the accuracy with which earthquakes can be located using high-quality seismic waveform data. This increased accuracy is due in large part to the use of waveform cross-correlation to measure the arrival times of seismic waves. With appropriate filtering the waveforms recorded at a seismographic station for different earthquakes are very similar, and waveform cross-correlation exploits this similarity to produce a very precise estimate of relative arrival time. These precise times can then be used in earthquake location algorithms that are specifically designed to use such data for highly precise estimates of relative earthquake locations. Such techniques have been used to produce spectacular images of faults and other sources of earthquakes such as the San Andreas Fault in California.

ANU has several datasets for which these techniques are likely to be very effective. These include data from a temporary seismograph deployment in the Flinders Ranges, one of the most active earthquake ‘hotspots’ in Australia (Figure 1). This data set includes around 500 locatable earthquakes, for which arrival times have been measured by conventional picking – i.e., ‘by eye’. While a few clusters are evident in the data, they form diffuse clouds, and it is not evident what kind of seismogenic structure might be generating these earthquakes. High-precision relative location techniques used with arrival times measured by cross-correlation are an ideal approach for bringing these clouds into sharper focus so that they can be more readily interpreted.

ANU has also collaborated with Geodynamics, Inc. on precise hypocenter of earthquakes induced as part of an experiment in the Coopper Basin on Enhanced Geothermal Systems (EGS).  This experiment involved pumping fluids into a deep borehole in order to develop a fracture system that would be conducive to the flow of fluid that could be extracted for purposes of geothermal energy extraction. Crucial to the success of such a project is the interaction of the facture network with the prevailing stress field and high pore pressures induced by the pumping, and theses interactions are most readily reveavled by high-precision earthquake hypocenter determinations. Again, cross-correlation arrival time measurements together with relative location techniques are an ideal way to learn more about these rock-fluid interactions that are critical to the successful extraction of geothermal energy in EGS.

In this project the student will learn about the processing of seismic waveform data and advanced earthquake location techniques.

Figure 1. Seismogrpah deployment and earthquake locations in the Flinders Ranges, SA. Left - distribution of seismic stations; Right - earthquake hypocentres, together with focal mechanim estimates.

Updated:  26 July 2017/Responsible Officer:  RSES Webmaster/Page Contact:  RSES Webmaster