1. Seismic Sources CEE 431/ESS465

2. Seismic Sources Identification Geologic evidence Field reconnaissance Trench logging Test pits, borings Airphoto interpretation Remote sensing Geophysics Historical seismicity

3. Seismic Sources Fault types

4. Seismic Sources Source zones May consist of mapped fault (known fault geometry) Areas of high seismicity Areas of shallow or outcropping bedrock Areas of sparse surficial vegetation May consist of diffuse zone (unknown fault geometry) Areas of low seismicity Areas with significant sediment cover Areas with dense vegetation cover California Washington

5. Seismic Sources Fault activity Active fault? NRC definitions require: Movement at or near the ground surface at least once within the past 35,000 yrs or movement of a recurring nature within the past 500,000 yrs Macroseismicity instrumentally determined with records of sufficient precision to demonstrate a direct relationship with the fault; or A structural relationship to a capable fault according to the previous two characteristics, such that movement on one could reasonably be expected to be accompanied by movement on the other

6. Seismic Sources Magnitude indicators M = f(E) E should increase with increasing dimensions of rupture surface Wells and Coppersmith (1994) Strike slipM w = 5.16 + 1.12 log L ReverseM w = 5.00 + 1.22 log L NormalM w = 4.86 + 1.32 log L AllM w = 5.08 + 1.16 log L Wells and Coppersmith (1994) Strike slipM w = 5.16 + 1.12 log L ReverseM w = 5.00 + 1.22 log L NormalM w = 4.86 + 1.32 log L AllM w = 5.08 + 1.16 log L Wells and Coppersmith (1994) Strike slipM w = 3.98 + 1.02 log A ReverseM w = 4.33 + 0.90 log A NormalM w = 3.93 + 1.02 log A AllM w = 4.07 + 0.98 log A Wells and Coppersmith (1994) Strike slipM w = 3.98 + 1.02 log A ReverseM w = 4.33 + 0.90 log A NormalM w = 3.93 + 1.02 log A AllM w = 4.07 + 0.98 log A

7. Seismic Sources Segmentation Earthquake segments - those parts of a fault that have ruptured during individual earthquakes Wasatch fault zone - Utah 8 segments Provo segment (70 km) longest Wasatch fault zone - Utah 8 segments Provo segment (70 km) longest

8. Segment length (or area) can constrain magnitude Segments bounded by discontinuities Geometric discontinuities - abrupt changes in strike, stepovers, gaps Structural discontinuities - fault bifurcations, zones of increased structural complexity, intersections with other structures Behavioral discontinuities - changes in slip rates, senses of displacement, creeping vs. locked behavior Seismic Sources Segmentation

9. Seismic Sources Puget Sound area Deep events Deep events Shallow events Shallow events

10. Seismic Sources Puget Sound area Known crustal faults Known crustal faults

11. Seismic Sources Puget Sound area Seattle fault Seattle fault

12. Seismic Sources Puget Sound area Intraplate source Intraplate source

13. Seismic Sources Puget Sound area Interplate source Interplate source