SHAKING “STABLE” CONTINENTS—PALEOSEISMOLOGY IN INTERIOR AUSTRALIA AND THE U.S

Earthquakes in stable continental regions (SCR) are infrequent compared to plate margins, but can be unusually destructive because the infrastructure is not designed and people are not prepared to withstand these rare shaking events. Because only 11 historical SCR earthquakes worldwide have produced documented surface rupture and SCR faults are typically aseismic prior to rupturing, it is difficult to assess the hazard that SCR faults pose.

To understand the long-term behavior of SCR faults and their associated hazard, we initiated our paleoseismic studies in Australia, where five of the 11 historical ruptures have occurred. Our targets were ruptures from the Ms 5.8, 1986 Marryat Creek, South Australia (SA), and Ms 6.3, 6.4, and 6.7, 1988 Tennant Creek, Northern Territory, earthquakes, and later, prehistoric scarps at Roopena, SA, and Hyden, Western Australia (WA). We found evidence of episodic behavior for SCR faults where tens to hundreds of thousands of years of quiescence separate intervals of clustered activity. This pattern has been corroborated by our further studies of the Meers fault, Oklahoma, the Cheraw fault, Colorado, and the Cadell and Meckering faults, in eastern and western Australia, respectively.

In the 1990s, only 13 potential Quaternary fault scarps were reported in Australia. However, recent analyses of 10-m-resolution DEM and SRTM data using digital-imaging software have helped identify more than 60 likely Quaternary faults in Western Australia alone. A less complete inventory, comprising many tens of more features, exists for the remainder of the Australian continent. This suggests that surface-rupturing SCR earthquakes, although infrequent, are typical. Australia’s generally arid climate helps preserve these fault scarps, whereas similar evidence of faulting may be obscured in more humid SCR settings. A systematic analysis of tectonic geomorphology could provide a complete inventory of Quaternary faults in all SCR settings, and paleoseismic studies could provide insight into the variability in their episodic behavior. Together, this information would contribute to improved assessments of seismic hazards in SCR settings such as Southern India, Southern and Western Africa, the central and eastern US, and Australia.