2008 National Seismic Hazard Maps

2008 National Seismic Hazard Maps-Fault parameters

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Fault Name	State
Rattlesnake-Wallula fault system	Washington

GEOMETRY
Dip (degrees)	60
Dip direction	SW
Sense of slip	reverse
Rupture top (km)	0
Rupture bottom (km)	15
Rake (degrees)	90
Length (km)	109

MODEL VALUES
Probability of activity	1
Minimum magnitude	6.5
Maximum magnitude	7.44
b-value	0.8

Assigned Dip	Fault-Parallel Slip Rate	Width	Annual Rate	a-value
60	0.05	17.3	1.73e-05	0.575

Comments
This zone of northwest-striking faults is assigned a lower slip rate in 2002 than in 1996. The zone of faults is mostly strike slip in its southeastern half and reverse in its northwestern half. Geomatrix Consultants, Inc. (1995) estimated a 0.8 probability that the entire system is reverse, dipping southwest, and a 0.2 probability that it is strike slip, dipping vertically. For each alternative, they published three fault-parallel slip rates and estimated the probability of each. For each of the six slip rates, we multiplied its probability by the probability of the associated faulting style, to obtain the probability of that combination of slip rate and faulting style. A fault-parallel slip rate of 0.05 mm/yr on a reverse fault is by far the most likely, having a probability of 0.48. The other five combinations ranged between 0.04 and 0.16. Geomatrix Consultants, Inc. (1995) estimated that fault dips of 45 and 60 degrees are equally probable. We chose 60 degrees. These values produce the assigned vertical slip rate of 0.043 mm/yr.

Comments

This zone of northwest-striking faults is assigned a lower slip rate in 2002 than in 1996. The zone of faults is mostly strike slip in its southeastern half and reverse in its northwestern half. Geomatrix Consultants, Inc. (1995) estimated a 0.8 probability that the entire system is reverse, dipping southwest, and a 0.2 probability that it is strike slip, dipping vertically. For each alternative, they published three fault-parallel slip rates and estimated the probability of each. For each of the six slip rates, we multiplied its probability by the probability of the associated faulting style, to obtain the probability of that combination of slip rate and faulting style. A fault-parallel slip rate of 0.05 mm/yr on a reverse fault is by far the most likely, having a probability of 0.48. The other five combinations ranged between 0.04 and 0.16. Geomatrix Consultants, Inc. (1995) estimated that fault dips of 45 and 60 degrees are equally probable. We chose 60 degrees. These values produce the assigned vertical slip rate of 0.043 mm/yr.