Back to CalendarProf. Rachel Abercrombie of Boston U. will present the EAPS Geophysics Seminar: Spatio-temporal variation in earthquake source properties on the San Andreas fault at Parkfield
“Small earthquakes contain a wealth of information about active structures, and the state of stress in the earth, not least because they are so numerous. Recent increases in the quantity and quality of seismic data, and computing power are enabling us to investigate these smaller events on scales not previously possible. The stress release (or stress drop) during an earthquake provides information about the energy budget, and the slip and area of rupture, which are needed to investigate earthquake triggering and rupture dynamics. Stress drop is also an important element of seismic hazard forecasting since high stress drop earthquakes radiate more high frequency energy, resulting in stronger ground shaking. In this talk I focus on the San Andreas Fault at Parkfield, where it transitions from locked to creeping segments. I present results from a detailed study of 3 repeating sequences, and a larger scale inversion for stress drop of over 4000 earthquakes, all recorded in shallow boreholes. I discuss resolution and uncertainties resulting from modelling assumptions and the ambiguity of separating source and path effects in recorded seismograms. I use the observations to investigate how earthquake rupture and average stress release depend on spatial and temporal changes in stress state, strain rate and slip conditions.”