Evidence for Fault Zone Trapped Waves from 1999 Hector Mine Earthquake Aftershocks
Marie Ammerman
UC Santa Barbara
marieammerman@hotmail.com
Mentor: Ralph Archuleta, UCSB
When an earthquake occurs within a fault,
it generates longer period waves, fault zone trapped waves (FZTW),
that arrive after the direct S wave. My project involves investigating
the source of these FZTW from aftershocks of the 1999 Hector Mine
earthquake. FZTW are generated by the lower velocities that characterize
the fault zone. When FZTW are observed, they reveal the
structure of the fault zone, including the width and the velocity
of the material within the fault zone.
FZTW can be differentiated from waves trapped in near surface low-velocity material by comparing the directions and phase velocities of the FZTW and the direct S waves. If it is concluded that the observed waves are FZTW, the maximum depth at which they are observed may show us the depth at which the fault becomes too thin to trap waves.
Seismograms from the Bullion Wash Array
will be analyzed for FZTW using Seismic Analysis Code. Seismograms
from earthquakes that occur both on and off the fault will be
compared to ensure that the waves are FZTW.
Table of Contents
Evidence for Fault Zone Trapped Waves
Pictures of the Surface Rupture
What are Fault Zone Trapped Waves
How waves travel through a fault zone
How fault zone trapped waves appear on a seismogram
Seismograms Without Fault Zone Trapped Waves
Differentiating from Basin Trapped Waves
Fault Zone Trapped Waves Tell Us About Fault Structure
Trapped Waves Show the Structure of Fault Junctions
Analysis Will Reveal the Velocity of the Fault Gouge
Geologic Cross Section Across the Bullion Wash Array
Will the Timing Corrections Help?