Quantifying Rupture Characteristics of Microearthquakes in the Parkfield Region Using a High-Resolution Borehole Network

Session: Earthquake Source Parameters: Theory, Observations and Interpretations
Type: Oral
Date: 4/30/2020
Time: 11:15 AM
Room: 120 + 130
Description: 

It is well known that large earthquakes often exhibit significant rupture complexity such as well separated subevents and directivity. With improved recording and data processing techniques, small earthquakes have been found to exhibit rupture complexity as well (e.g., Wang et al. 2016). Studying these small earthquakes offer the opportunity to better understand the possible causes of rupture complexities. Specifically, if they are random or are related to fault properties. To better understand the factors that influence rupture complexity behaviors, we examine microearthquakes in the Parkfield area that are recorded by the high-resolution borehole networks. The Parkfield area is chosen because it is a densely studied region with well documented structural and lithological features that the results of this work can be compared to. We quantify earthquake complexity first by computing the Source Time Functions (STF) of those events that can be accurately resolved. STFs allow us to clearly identify subevent occurrence for only the best recorded events and can only be made for small portion of events. To obtain estimates of rupture complexity for more events, we also quantify event complexity by quantifying how much their source spectra deviate from Brune-type source models following the method of Uchide and Imanishi (2016), based on the hypothesis that events that show strong deviations from the simple circular rupture model prediction may contain rupture complexity. These two methods used in combination allows for the confirmation of complexity between both methods and further understanding of complexity observed in spectra. To explore possible causes of rupture complexity (or lack of), we examine the coseismic slip models of the 2004 Parkfield Mw 6.0 earthquake, geological structures from fault and velocity models, as well as creep rate changes along the Parkfield segment.

Presenting Author: Colin N. Pennington

Authors