Implications of Temporal Clustering and Long-Term Fault Memory for Earthquake Forecasting

Date: 4/24/2019

Time: 05:00 PM

Room: Pike

A major challenge for earthquake forecasts is that geologic records often show large earthquakes occurring in temporal clusters separated by periods of quiescence. If we are in the cluster, a large earthquake may happen soon. If we are between clusters, a great earthquake is less likely soon. Clusters are observed in paleoseismic records in a variety of tectonic settings, from subduction zones to intraplate regions. While clusters, sometimes known as supercycles, could be artifacts of the limits of the paleoseismic record, they appear in enough records that they warrant the attention of forecasters. The existence of clusters is problematic for long-term forecasts because it implies that the system is not stationary, and therefore traditional probability models do not apply. The cause of these clusters is unclear, and the traditional earthquake cycle model does not explain them. We are exploring an alternative model for the occurrence of large earthquakes, Long Term Fault Memory (LTFM). In LTFM, the probability of an earthquake grows with time at a steady rate, simulating steady strain accumulation. The probability drops after an earthquake, but does not necessarily reset to zero as in the traditional earthquake cycle model, simulating a partial strain release. This allows the fault’s history over multiple cycles to influence the future probability of an earthquake. We use LTFM to simulate paleoseismic records from subduction zones, transform faults, and intraplate regions, including a particularly long record from the Cadell fault in intraplate Australia, exploring the similarities and differences between these regions. In some portions of the simulated earthquake history, events can appear quasi-periodic, while at other times, the events can appear more Poissonian. Hence a given paleoseismic or instrumental record may not reflect the long-term seismicity of a fault, which has important implications for hazard assessment.

Presenting Author: Leah Salditch

Authors