Station-Specific
Traveltime Tables In a 3D earth
Goal:
improve earthquake locations
while
minimizing computation effort through
precomputation
Three-D earth model
elliptical earth model
½ degree resolution, tetrahedral splines
based on available structural information
Crust 2.0
Pn tomography
Surface wave tomography
Overall
organization into
interfaces
Small-scale
organization into
tetrahedra
Linear interpolation
within tetrahedra
implying rays that
are circular arcs
First Cut at building a 3-d MODEL
Simplified, 2-layer-crust version of Crust 2.0
on top of AK135 mantle
with sub-Moho velocities adjusted to match
Crust 2.0 Pn velocities
Strategy
Compute differential traveltimes between
3D model
and
reference vertically-stratified model
one traveltime calculation for each station
gives traveltime correction for earthquake
anywhere in the US to that station
Examples
Crust2 minus AK135
differential traveltimes
Shadow
zone
Sensitivity Test
Test grid of earthquake hypocenters
Current US station configuration
Traveltimes for 3D model
Location using AK135
Assess location error
Stations east of California
Location Errors:
= 0.5 degree
Note: this preliminary calculation used data from a
limited number of stations