Earthquake Rate Models on A faults

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Earthquake Rate Models on A faults In Northern
California for the National Seismic Hazard Maps
and Working Group on California Earthquake
Probabilities
Menlo Park, CA January 17, 2007
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• Types of earthquake recurrence models considered
• Segmented models from WG 2002
• B-fault type models as used by NSHMP

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A fault Major fault with high slip rates and
sufficient data on slip rates, timing of past
events, and slip per event that detailed models
of fault zone behavior can be constructed B
fault Faults that have significant slip rates
but inadequate data on displacement or timing of
past earthquakes to constrain detailed fault
models C fault Zone of distributed shear with
defined slip rate from geodetic and plate model
where earthquakes may occur on recognized or
unrecognized faults.
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Characteristic earthquakes on a segment of an A
fault

• Parameters
• Slip rate
• Characteristic or maximum magnitude
• Epistemic and aleatory uncertainty

Log N(m)
Wt.6
Wt.2
Wt.2
0.2
0.12
magnitude
mchar
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USGS Magnitude-frequency model for B-faults

• Parameters
• Slip rate
• Characteristic or maximum magnitude
• Epistemic and aleatory uncertainty
• Ratio of Characteristic to Floating Rupture
  moment rate
• Minimum magnitude
• b-value

2/3 Moment rate split into three magnitudes 1/3
Moment rate for floating ruptures (GR)
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• Development of earthquake rate models
• Earthquake rates depend on slip rates and are as
  consistent as possible with paleoseismic data.
• All segments and combinations of segments have
  rates of earthquakes in three models
• Minimum earthquake rate model
• Maximum earthquake rate model
• Geologic insight model
• Southern San Andreas based on detailed numeric
  analysis by Weldon and Biasi
• Other A-faults based on hand-built models due
  to sparse data

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Example, Calaveras fault, modifications WG2002
model to remove floating, sub-segment ruptures.
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Key question, and only significant modification
to earthquake rate models How to incorporate
Recurrence Data from Arano Flat in the Santa Cruz
Mountains. RI at Arano Flat is 105 yr,
approximately half RI of full-segment and
multi-segment ruptures predicted there by
WG02. Is there a small segment here with
frequent smaller earthquakes? Are these
sub-segment earthquakes? Are all of these full
segment or multi-segment earthquakes?
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Rates of full-segment and multi-segment
earthquakes on the Northern San Andreas fault, if
5, 7, or 9 of the 9 earthquakes at Arano Flat are
full- or multi-segment ruptures.
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