Station-Specific Traveltime Tables In a 3D earth

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Station-SpecificTraveltime Tables In a 3D earth
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• Goal
• improve earthquake locations
• while
• minimizing computation effort through
  precomputation

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• 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

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Overall organization into interfaces
Small-scale organization into tetrahedra
Linear interpolation within tetrahedra implying
rays that are circular arcs
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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
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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

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ExamplesCrust2 minus AK135differential
traveltimes
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Shadow zone
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Sensitivity Test

• Test grid of earthquake hypocenters
• Current US station configuration
• Traveltimes for 3D model
• Location using AK135
• Assess location error

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Stations east of California
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Location Errors 0.5 degree
Note this preliminary calculation used data from
a limited number of stations