UCL Institute for Risk and Disaster Reduction


Mohamed Alwahedi

Time series analysis of borehole strainmeter data in the western US reveals coseismic and postseismic surface deformations associated with intermediate magnitude earthquakes (M4-6)

  • Supervisor: Peter Sammonds and Katerina Stavrianaki
  • Funding: Ministry of Education – United Arab Emirates
  • Email: m.alwahedi.17@ucl.ac.uk

In my undergraduate project, 112 earthquakes were processed and interpreted to analyse their postseismic strain. Interpreted earthquakes were followed by afterslip, releasing 20-60% of the moment of the coseismic deformation in the 20 minutes to 1.5-day period following the main shock, with 70% confidence intervals. These postseismic to coseismic strain ratios are consistent with previous studies on intermediate magnitude earthquakes (i.e. if considering the same postseismic time interval). Additionally, these results are slightly higher than aseismic slip released after large earthquakes (M > 6), but lower than observed after small earthquakes (M < 4).

My target is to examine the relation between postseismic and coseismic strain at different locations in order to cover other fault types. For instance, Japan and Italy to check if the hypothesis is only restricted to California or is a general phenomenon. Furthermore, the project could be linked to seismicity and associated hazard if the link between high postseismic rates and aftershocks has been proven. If moderate earthquakes release higher postseismic slip, which is positively correlated with aftershocks as suggested by Hsu et al. (2006), then we should re-evaluate our hazard plans as some intermediate earthquakes have caused unexpected damage in the past, e.g. South Napa earthquake (M6).