U.S. National Seismic Hazard Maps – Intermountain West Source Models

1. U.S. National Seismic Hazard Maps – Intermountain West Source Models Mark Petersen and YuehuaZeng

2. What can we do in 5, 10, and 20 years to improve earthquake source models in the IMW? • Use available geodetic data in hazard maps (determine experiment to quantify discrepancy between geodetic strain rates, geologic slip rates, paleoseismic earthquake rates; e.g., explain by post-seismic slip, smaller earthquakes, aseismic slip, uncertainties) • New fault information (locations, slip rates, paleoseismic rates, magnitude-frequency distribution) • Find ways to make model and historic earthquake rates compatible

3. Geodetic strain rates • Does the current 10-15 year GPS rate represent long-term average rates? • How sensitive are results to model parameters (the locking depth, parameters in block models)? • How can we partition strain-rate data onto individual faults in complex zones with closely spaced faults? • How can we quantify the portion of strain-rate released in large damaging earthquakes? How do we translate strain rates to earthquake rates? • What are uncertainties in data and results?

4. Geologic slip rates • Does the current rate represent long-term average rates? (creep rates) • What are uncertainties in the offsets and timing? (in CA most are moderate to poorly constrained) • How can we quantify the portion of fault slip rate released in large damaging earthquakes? How do we translate slip rates to earthquake rates? • What are uncertainties in data and results?

5. Paleoseismic Data • Are all events seen in a trench? How many trenches do we need to characterize earthquake rates? • How do we explain clustered earthquakes? Does this imply variable slip rate on fault? • What are uncertainties in event timing? • Are trenches over-interpreted indicating too many events? • What are uncertainties in data and results?

6. Needs of NSHMP • 1. Characterize hazard in urban areas (Reno/Carson City and Lake Tahoe); 2. understand hazard in other areas • Understand differences in strain rates from geologic and geodetic data – how do we translate strain rates to earthquakes • Interpret distribution of strain through Walker Lane – both long-term and modern

7. Goal • To develop one model that satisfies the geologic, geodetic, and paleoseismic data best and other models that encompass range of uncertainties • If not possible then compromise with alternative weighted models

9. Modeling Source Zones • Strain rate converted to moment rate (Kostrov, 1974) • Geodetic zones (C zones) shapes based on block model • Rates for Zones 2-4 based on composite of seismicity, geologic, and geodetic rates (suggested by WSSPC advisory panel) • We used 50% of the residual shear rate • Two new zones added in S CA (Mojave and San Gorgonio Pass)

10. C-Zones

11. 2 mm/yr, M 6.5-7.3 strike=-25 b=0.8 Surprise Valley 1.3 Hat Creek, McCarther, Cedar Mtn 1-1.5 mm/yr 2 mm/yr M 6.5-7.3 strike=-45 b=0.8 Honey Lake 2.5 mm/yr 4 mm/yr M 6.5-7.3 strike=-45 b=0.8 0.05 mm/yr M 6.0-7.0 strike=-35 b=0.9 1 mm/yr Genoa Antelope V. 4-5 mm/yr Death Valley White Mountains