summary of shoreline fault - a4nra4nr.org/.../2010/05/...shoreline-fault-slide-show.pdf · schedule...
TRANSCRIPT
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Summary of Shoreline Fault Lloyd Cluff and Norman Abrahamson
PG&E Geosciences Department June 10, 2009
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Summary of Shoreline Fault
Alignment of epicentersoffshore DCPP
Alignment
DCPP
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2008 USGS Marine Survey Area
Blue – 800 m Seismic/ Magnetic
Orange – 400 m Magnetic
Summary of Shoreline Fault
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Comparison of Earthquake Locations with Marine Magnetic Data
DCPP
Courtesy, Janet Watt (USGS)
Hosgri fault zone
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Seismicity cross sectionsOctober 1987
toMarch 2007
Earthquake locationscourtesy of J. Hardebeck (USGS)
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Earthquake locationscourtesy of J. Hardebeck (USGS)
Black: good quality single- event mechanisms
Gray: lower quality single- event mechanisms
Red: composite mechanisms
Focal mechanismsshow predominantly strike-slip motionin the offshore region
DCPP
Hosgri fault zone
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Initial Evaluation of Seismic Demands from Assumed Shoreline Fault Zone
• Magnitude– Based on the size of the fault
• 24 km length (extended to the intersection with Hosgri)• 12 km depth
– M = 6.5
• Distance– 1 km from DCPP (assumed)
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Initial Evaluation of Ground Motion (84th Percentile Deterministic)
Assumed Shoreline Fault Zone
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Summary of Shoreline Fault
Assumed Shoreline Fault
– Methods to estimate and constrain:
Location Variations in seismicity alignment Style of faulting Length and rupture area Magnitude of potential earthquakes Constraints on activity and fault slip-rate
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Summary of Shoreline Fault Action Plan
• Assumed Faults Length and Width– Does Shoreline fault zone extend to Hosgri?– Does Shoreline fault zone extend to the SE?– Is the fault zone continuous over its length
• Fault zone may be broken into small discontinuous segments
• Closest distance offshore DCPP– Assuming 1 km, could be less– Epicenters uncertain to 1 km
• Activity Rate– Slip-rates not available yet– Appear to be low
Topics being reviewed in PG&E’s Action Plan
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Summary of Shoreline Fault
• Synchronous rupture of Hosgri and Shoreline FZ (splay)?– Geometry is unfavorable for Splay faulting
• Rupture stepping from Hosgri onto Shoreline FZ ?– Rupture Length would be reduced
• North end of Hosgri (San Simeon Flt) to SE end of SFZ is about 60 km• M=6.85 (W=12), M=7.0 (W=16)
– Distance to DCPP• Offshore geophysical data needed to constrain the location offshore
and the distance to DCPP
Topics being reviewed in PG&E’s Action Plan
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Summary of Shoreline Fault
Ground Motion Sensitivity (emp)
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Summary of Shoreline Fault
There appears to be various alignments
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Pt. Buchon Multibeam Bathymetry
collected as part ofCA State Waters Mapping Program by CSU Monterey BaySeafloor Mapping Lab 2006-2007
Summary of Shoreline Fault
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Summary of Shoreline Fault
Paleo-wave-cut platforms
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Summary of Shoreline Fault
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Summary of Shoreline Fault
LTSP - Small Faults in Southwest Boundary Zone
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Summary of Shoreline Fault
Wave-cut Shorelines near DCPP usedas Strain Gauges to Constrain Fault Deformation
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Summary of Shoreline Fault
Predicted Paleoshorelines in Point Buchon Area
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Summary of Shoreline Fault
Geologic Map of Point Buchon Area
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Summary of Shoreline Fault
50,00050,000--yearyear--old old wavecut platform wavecut platform
across the N40W Faultsacross the N40W Faults
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Summary of Shoreline Fault
Within Data resolution, Paleo-Platform is not Deformed
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Summary of Shoreline Fault
Seismic Line PBS-32 Across the N40W Faults
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Summary of Shoreline Fault
Hosgri fault
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Summary of Shoreline Fault
2009 Multibeam Survey Area
3 priority areas
1. Shoreline ‘surf zone’ 0 – 10 m2. Pecho Fault Zone 10 – 50 m 3. Hosgri Fault Zone 50 – 150 m
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Schedule for Shoreline Fault Studies
Schedule for 2009 Activities• July 2009
– Complete offshore geophysical data collection• August 2009
– Complete peer review of USGS seismicity studies• November 2009
– Complete initial integration of new offshore geophysical data with the magnetic, seismic, geologic, and gravity data
– Updated interpretation of geometry, segmentation, and slip-rate of the SFZ
– Estimate ground motion at DCPP for possible rupture stepping from Hosgri to SFZ
• December 2009– Issue interim report to NRC summarizing updated information and
interpretation (source characterization and ground motion)
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Schedule for Shoreline Fault Studies
Schedule for 2010 Activities• June 2010
– Complete geologic mapping of onshore faults that may interact with the SFZ
– If needed, collect additional offshore geophysical data• November 2010
– Complete final integration and interpretation of offshore geophysical data with the magnetic, seismic, geologic, and gravity data to characterize the SFZ
– Complete final estimate of deterministic ground motions at DCPP for the updated characterization of the SFZ
– Complete updated probabilistic seismic hazard analysis• December 2010
– Issue final report to NRC summarizing updated information and interpretation of the SFZ
• Location, geometry, segmentation, and activity rate• Ground motions at DCPP (deterministic and probabilistic)
• Note: Results will be incorporated into the updated tectonic model for the region to be completed 2012