Diversity of Earthquake Source Processes in Minto Flats Fault Zone, Central Alaska

Session: From Aseismic Deformation to Seismic Transient Detection, Location and Characterization [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Regular earthquakes are traditionally described as starting abruptly with no activity immediately preceding the p-wave arrival. Many earthquakes in the Minto Flats Fault zone (MFFZ) in interior Alaska do not fit the traditional description and instead have a variety of pre-mainshock signals associated with them. We qualitatively describe the various signals and place each event into one of four categories: (1) regular earthquakes that have an abrupt p-wave arrival and no activity directly preceding the event, (2) events with a gradual nucleation signal that have an abrupt p-wave but also exhibit some 20 or fewer seconds of increasing activity above the noise level, (3) events with a non-abrupt p-wave arrival that do not necessarily exhibit pre-mainshock activity but instead resemble very-low-frequency earthquakes and (4) events with identical foreshock activity that have abrupt p-wave arrivals but are immediately preceded by a smaller event that is identical to the mainshock. We quantify this classification process by estimating a small set of parameters to fit the log-scaled envelope of 2–8 Hz filtered seismograms for each recording in the MFFZ. The envelope is sensitive to high frequencies allowing us to see exactly when earthquake activity rises above background noise; this is particularly useful in the MFFZ due to higher noise levels caused by a river and the surrounding sedimentary basin. Once identified and described, we relocate each event in the region to examine the spatial relationships among the various types of events. The observational analysis is augmented by rate-and-state numerical modeling of the MFFZ. Numerical simulations are able to represent a wide range of observed behavior in the MFFZ, including repeating foreshocks, nucleation growth and swarms. We propose that a narrow range of fault friction parameters can represent the diversity of observations in the MFFZ, suggesting that the MFFZ may be exceptional among instrumented fault zones worldwide.

Presenting Author: Nealey Sims

Authors