View
3
Download
0
Category
Preview:
Citation preview
Summary of Shoreline Fault Lloyd Cluff and Norman Abrahamson
PG&E Geosciences Department June 10, 2009
2
Summary of Shoreline Fault
Alignment of epicentersoffshore DCPP
Alignment
DCPP
3
2008 USGS Marine Survey Area
Blue – 800 m Seismic/ Magnetic
Orange – 400 m Magnetic
Summary of Shoreline Fault
Comparison of Earthquake Locations with Marine Magnetic Data
DCPP
Courtesy, Janet Watt (USGS)
Hosgri fault zone
5
Seismicity cross sectionsOctober 1987
toMarch 2007
Earthquake locationscourtesy of J. Hardebeck (USGS)
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
7
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)
8
Initial Evaluation of Ground Motion (84th Percentile Deterministic)
Assumed Shoreline Fault Zone
9
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
10
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
11
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
12
Summary of Shoreline Fault
Ground Motion Sensitivity (emp)
13
Summary of Shoreline Fault
There appears to be various alignments
14
Pt. Buchon Multibeam Bathymetry
collected as part ofCA State Waters Mapping Program by CSU Monterey BaySeafloor Mapping Lab 2006-2007
Summary of Shoreline Fault
15
Summary of Shoreline Fault
Paleo-wave-cut platforms
16
Summary of Shoreline Fault
17
Summary of Shoreline Fault
LTSP - Small Faults in Southwest Boundary Zone
18
Summary of Shoreline Fault
Wave-cut Shorelines near DCPP usedas Strain Gauges to Constrain Fault Deformation
19
Summary of Shoreline Fault
Predicted Paleoshorelines in Point Buchon Area
20
Summary of Shoreline Fault
Geologic Map of Point Buchon Area
21
Summary of Shoreline Fault
50,00050,000--yearyear--old old wavecut platform wavecut platform
across the N40W Faultsacross the N40W Faults
22
Summary of Shoreline Fault
Within Data resolution, Paleo-Platform is not Deformed
23
Summary of Shoreline Fault
Seismic Line PBS-32 Across the N40W Faults
24
Summary of Shoreline Fault
Hosgri fault
25
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
26
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)
27
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
Recommended