Earthquake Predictibility, Forcasting and Early Warning

1. Earthquake Predictibility,Forcastingand Early Warning Bill Menke October 18, 2005

2. Summary Are long-term predictions of earthquakes possible? Are short short-term (or intermediate term) predictions of earthquakes possible? Can specific earthquakes be forecast? Are a few seconds or minutes of Early Warning useful. Is rapid assessment useful?

3. Why might long-term predictions be possible ? Most earthquakes are on plate boundaries Plate motions are very constant over long periods of time Faults at plate-boundaries are long term features Long-term fault slip rate of faults are fairly constant Segments of faults seem to rupture time and time again in similar earthquakes Earthquake occurs when loading exceeds strength

4. Long-term Predictability Most earthquakes are on plate boundaries

5. Long-term Predictability Plate motions are very constant Here are the current-day plate motions as measured by GPS satellite geodesy

6. But present-day rates (black) agree very well for averages for the last million years, as determined from geological features (red)

7. San Andreas Fault System Pacific-North America plate motion: 4.8 cm/year Part of slip accommodated by San Andreas: 2.9 cm/year Long-term Predictability Faults at plate-boundaries are long term features

8. Long-term Predictability Faults at plate-boundaries are long term features 23.5 Ma Volcanic rocks offset by 315 km, rate of 1.3 cm/year

9. Almost no new faults Faults grow slowly A big earthquake on a fault tends to increase the length of the fault The bigger the fault, the bigger the earthquake that can occur

10. Strategy: map the faults to determine where earthquakes will occur (but look for evidence of recent motion, make sure it’s a recently active fault)

11. Problem: deeply buried faults, such as blind thrusts(especially if they have few small earthquakes) (example fault that caused 1994 Northridge Earthquake) (But now we know it’s there!)

12. Long-term Predictability Faults segmentation: characteristic large earthquakes

13. Example – Parkfield Segment of San Andreas Fault

14. 2004 History of 7 large earthquake that broke the segment

15. Segmentationin Japan

16. Loading rate correlates With plate-tectonic motions Maximum load Long-term Predictability Earthquake occurs when loading exceeds strength loading Eq Eq Now: where Are we in the Loading cycle ? time, years

17. Earthquakes on neighboringfaults change loading but can beaccounted for Northern Anatolian Fault (strike-slip) in Turkey Portions of fault that recently experience large earthquakes are far from failure But neighboring portions are driven closer to failure

18. Loading in California since 1812, incl. plate motions and large eqs. Note most small earthquakes (circular symbols) occurred in high-load areas

19. Results of this kind of analysis Is a prediction of likelihoof of a large earthquake on each Of a region’s fault Assuming: long-term loading rates determined by GPS and/or geological studies and closeness to failure based on when last large event occured

20. Why might short-term or intermediate-term predictions be possible ? Detectable changes in fault behavior as it approaches failure Examples: Foreshocks – small earthquakes that occur before the big one – short term Seismicity rate changes – increase in rate of moderate earthquakes prior to the big one – intermediate term

21. Foreshock little one before the Big One • In California, foreshocks occur less than 5 days before about half of the large earthquakes. For these reasons, the California Office of Emergency Services issues an advisory of an increased likelihood of a major earthquake within the next 5 days following moderate-sized earthquakes.

22. Northern California: Rate and pattern of moderate earthquakes not constant with time

24. What can you do with a prediction of an earthquake ?Especially if it has low skill

25. Short term heightened emergency preparedness curtain endangered activities evacuate people Intermediate term redirect preparedness funds re-site future construction

26. Early Warning- or every second counts -

27. How long do you have ? city Strong ground motion sensors 10 km 50 km 50 km distant At 2 km/s shear wave velocity Is 25 seconds Minus 10 seconds to Detect strong motion at a Few stations near fault Is … fault

28. 15 seconds

29. But say the damaging effects extend to 100 km … 50 km 100 km < 15 second warning > 15 second warning … There may be a lot of people & structure in the >15 second warning region area

30. For this to have any hope of workingyou must plaster the earth withsensors capable of detecting strong ground motion and immediately sending that information to a processing and distribution center

31. Seismic Intensity Stations in Japan

32. So little time is availablethat both theannouncement of impending strong shakingand the responsemust be fully automated

33. What can you do in 15 seconds ?Shut down delicate or dangerous equipmentHave people dive for shelter (?)

34. Just knowing where the strong shaking occurredcan help in formulating an emergency response Strong ground motions after the 1995 Kobe, Japan earthquake