Effect of Velocity Models on the Accuracy of Earthquake Hypocenters
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Effect of Velocity Effect of Velocity Models on the Accuracy Models on the Accuracy of Earthquake of Earthquake Hypocenters Hypocenters Sudipta Sarkar, Youshun Sun, M. Nafi Sudipta Sarkar, Youshun Sun, M. Nafi Toks Toks ö ö z z Earth Resources Laboratory Earth Resources Laboratory Massachusetts Institute of Massachusetts Institute of Technology Technology USA USA
description
Effect of Velocity Models on the Accuracy of Earthquake Hypocenters. Sudipta Sarkar, Youshun Sun, M. Nafi Toks ö z Earth Resources Laboratory Massachusetts Institute of Technology USA. Big Picture. Earthquake hypocenters could be in error by tens of kilometers - PowerPoint PPT Presentation
Transcript of Effect of Velocity Models on the Accuracy of Earthquake Hypocenters
Effect of Velocity Models on Effect of Velocity Models on the Accuracy of Earthquake the Accuracy of Earthquake
HypocentersHypocenters
Sudipta Sarkar, Youshun Sun, M. Nafi ToksSudipta Sarkar, Youshun Sun, M. Nafi Toksöözz
Earth Resources LaboratoryEarth Resources Laboratory
Massachusetts Institute of TechnologyMassachusetts Institute of Technology
USAUSA
Big PictureBig Picture
Earthquake hypocenters could be in Earthquake hypocenters could be in error by tens of kilometerserror by tens of kilometers
Several factors contribute to errorsSeveral factors contribute to errors– Poor station coveragePoor station coverage
– Phase reading errorsPhase reading errors
– Poor knowledge of velocityPoor knowledge of velocity
– Lateral variations of velocityLateral variations of velocity
OutlineOutlineEarthquake location errors due to errors in Earthquake location errors due to errors in velocity models: Examples -velocity models: Examples -
I.I. Local scaleLocal scale
II.II. Regional scaleRegional scale
Improving location accuracy by using a 3D Improving location accuracy by using a 3D velocity modelvelocity model
China caseChina case
A practical approach to improving location A practical approach to improving location accuracyaccuracy
Source Specific Station correctionSource Specific Station correction
Applicability to the Gulf regionApplicability to the Gulf region
ConclusionsConclusions
Velocity Model and Depth of EventsVelocity Model and Depth of Events
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Velocity Model and Depth of EventsVelocity Model and Depth of Events
Velocity Model and Depth of EventsVelocity Model and Depth of Events
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Depth Error in Local Events Due to Depth Error in Local Events Due to Incorrect Velocity ModelIncorrect Velocity Model
Vel #1 Vel #2 Vel #3
1D1D(km)(km)
AK135AK135(km)(km)
11 Events 11 Events (Explosions)(Explosions)
1010 2020
EarthquakeEarthquake 1212 2020
Location Errors Due to Lateral Location Errors Due to Lateral Variation of VelocityVariation of Velocity
Our experience in CHINA
3D3D(km)(km)
1D1D(km)(km)
AK135AK135(km)(km)
11 Events 11 Events (Explosions)(Explosions)
11 1010 2020
EarthquakeEarthquake 3.53.5 1212 2020
Location Errors Reduced by Location Errors Reduced by Introducing a 3D ModelIntroducing a 3D Model
Our experience in CHINA
Event Relocation Using 3D Travel Event Relocation Using 3D Travel Times: A Regional Study in ChinaTimes: A Regional Study in China
MethodMethod
Determine 3-D, regional velocity Determine 3-D, regional velocity structure in crust and upper mantle structure in crust and upper mantle (tomography)(tomography)
Use 3-D velocity / travel time grids to Use 3-D velocity / travel time grids to locate eventslocate events
A Regional Study in ChinaA Regional Study in China
A Regional Study in ChinaA Regional Study in China
A Regional Study in ChinaA Regional Study in China
3D3D(km)(km)
1D1D(km)(km)
AK135AK135(km)(km)
11 Events 11 Events (Explosions)(Explosions)
11 1010 2020
EarthquakeEarthquake 3.53.5 1212 2020
Location Errors Reduced by Location Errors Reduced by Introducing a 3D ModelIntroducing a 3D Model
Our experience in CHINA
Station Distribution and Events in Station Distribution and Events in the Gulfthe Gulf
Prospects of 3D Tomography and Prospects of 3D Tomography and Event Location in the GulfEvent Location in the Gulf
A Practical ApproachA Practical ApproachDoing true 3D locations is Doing true 3D locations is computationally expensive and most computationally expensive and most often not possible!often not possible!
A practical solution to this problem – A practical solution to this problem – use use Source Specific Station Corrections.Source Specific Station Corrections.
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Dijij ttttSC 3
ProcedureProcedureUse 3-D velocity models to calculate Use 3-D velocity models to calculate travel times from all potential source travel times from all potential source regions to all stationsregions to all stations
Determine source specific station Determine source specific station corrections relative to reference model corrections relative to reference model used for locationsused for locations
Determine an initial locationDetermine an initial location
Apply the station correction to times at Apply the station correction to times at each station specific for the source each station specific for the source regionregion
Relocate the eventRelocate the event
ConclusionsConclusionsLocal and regional seismic networks are Local and regional seismic networks are improving rapidlyimproving rapidly
Accurate event locations with these networks Accurate event locations with these networks require accurate 3D velocity modelsrequire accurate 3D velocity models
Such velocity models can be derived through Such velocity models can be derived through regional seismic tomographyregional seismic tomography
3D travel times can be implemented through 3D travel times can be implemented through source specific travel time correctionssource specific travel time corrections
New networks in the Gulf region provides an New networks in the Gulf region provides an opportunity for 3D velocity models and more opportunity for 3D velocity models and more accurate locationsaccurate locations
