Spectral and Temporal Evolution of Surface Creep Events in Parkfield, 1990-Present

Date: 4/26/2019

Time: 02:00 PM

Room: Vashon

Creepmeters and strainmeters permit the depth evolution of shallow creep events to be quantified as they propagate along strike. To complete describe a transient episodic creep event requires constraints on depth, area, and velocity and the evolution of all these three parameters with time. In recent work we have found it possible to define the properties of an aseismic slip event using just three parameters - an initiation time (t0), a time constant (w) and a slip velocity (vp). This combination, constrained from observations of multiple events at known locations and invoking simple assumptions about planar fault geometry, allows for the characterization of static and dynamic spatial-temporal behavior of creep events. We develop a quasi-dynamic model and code to exploit this and to apply it successfully to observed creep events. Detection of creep events has hitherto been accomplished by visual inspection. Our new method permits us to use these parameters and machine learning methods to detect creep events. Our previous investigations have been confined to studies where creep events were simultaneously observed on strainmeters and creepmeters allowing for constraints on area and average depth, here we apply this analysis to using surface creep data alone. We demonstrate the method on a catalog of ~6000 creep events observed on three creepmeters (XMM1,XMD1,XVA1), located near Parkfield on the creeping section of the San Andreas Fault, between 1984-2018 including the September 28, 2004, M6.0 Parkfield event. We show that while the total creep rate on creepmeters near Parkfield is similar before and after the 2004 earthquake (excluding a four year period of afterslip), that there is a evolution and change of the dynamic behaviour of creep events, in particular the time constant (w), during the observation period.

Presenting Author: David Mencin

Authors