SCEC Award Number 11200 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Stress Drop and Source Description for Earthquakes 4 < M < 5.5 in Southern California
Investigator(s)
Name Organization
Ralph Archuleta University of California, Santa Barbara
Other Participants Jorge Crempien
SCEC Priorities B3, B5, B4 SCEC Groups Seismology, GMP, FARM
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
 Using short-period P waves, Shearer et al. (2006) estimated stress drops for ~65,000 earthquakes with 1.6 The northern end of the El Mayor earthquake was particularly active in producing earthquakes with Mw>4. The epicenters are in a region where stress drops as low as ~0.6 MPa would be expected. Aftershocks, with 4.0
Intellectual Merit The state of stress in the Earth is a fundamental quantity for understanding how and why earthquakes occur, how faults interact and the source of radiation. However, the absolute state of stress is not directly measurable from earthquakes, only the change in stress (stress drop). The stress drop is highly variable locally; but the median is generally stable but variable from location to location. This variability at a particular location and from place to place is not understood. However, any dynamic model of an earthquake should reproduce this variability which will have direct consequences for ground motions computed from earthquake simulation.
Broader Impacts The ground motion computed with SCEC simulators depend on realistic input parameters. These parameters are derived from analysis of real events. The ground motion estimates from the simulations are used to guide the development engineering design. This research is directly related to the larger SCEC program in broadband simulations. This research is the underpinning of those simulations.
Exemplary Figure Fig. 5. Histogram that shows the variability of observed stress drops. The average is shown in the red solid and dashed line, with a value of 0.89 and 1.51 MPa for the downhole and surface recordings respectively. The ± 1 standard deviation is shown in the green solid and dashed lines, with a standard deviation value of 4.38 and 5.78 MPa for the downhole and surface recordings respectively.