Hypothesis:

1. The Parkfield Experiment is a comprehensive, long-term earthquake research project on the San Andreas fault. The experiment's purpose is to better understand the physics of earthquakes - what actually happens on the fault and in the surrounding region before, during and after an earthquake Prediction by USGS in April, 1985:"A 90% probability of an earthquake with Magnitude 5.5 to 6.0 occurring sometime between 1985 and 1993."

2. The San Andreas fault defines an approximately 1300 km portion of the boundary between the Pacific and North American plates. Along its length, the fault undergoes horizontal strike-slip motion that accommodates most of the relative motion between the plates. To the north, a complex of transform faults and spreading centers accommodates the motion of the Gorda and Juan de Fuca plates. To the south, a similar complex of spreading centers and transform faults accommodate the displacement in the Gulf of California.

3. Hypothesis: • Moderate-size earthquakes of about M6 have occurred on the Parkfield section of the San Andreas Fault at fairly regular intervals. • EQ’s 1857, 1881, 1901, 1922, 1934, 1966, and finally in 2004. • The first EQ, in 1857, was a foreshock to the great Fort Tejon earthquake which ruptured the fault from Parkfield to the southeast for over 180 miles.

4. Foreshocks and Aftershocks The size of the aftershocks depends on the size of the initial large earthquake Press et al., 2004

5. Two Big Questions: *What causes earthquakes to start in specific locations? *What causes earthquakes to stop in specific locations? Three Big Possible Answers: *Fault Zone Rheology Friction, Deformation Styles *Fault Zone Stress Conditions Tectonics, Stress Triggers/Shadows, Pore-pressure *Fault Zone Geometry Fault Continuities and Discontinuities March 2006 WGCEP Workshop

6. Available data suggest that all six moderate-sized Parkfield earthquakes may have been "characteristic” • The EQ’s all ruptured the same area on the fault. • If such characteristic ruptures occur regularly, then the next quake would have been due before 1993. • However, the predicted earthquake still occurred in September 2004.

7. The San Andreas fault in central California. • A "creeping" section (green) separates locked stretches north of San Juan Bautista and South of Cholame. • The Parkfield section (red) is a transition zone between the creeping and southern locked section. • Stippled area marks the surface rupture of the 1857 EQ

8. The central/creeping segment experiences numerous small earthquakes, usually with M < 4.0. The Calaveras and Hayward Faults east of San Francisco Bay show a similar pattern. Left: The San Andreas Fault as it cuts just to the south of the town of Parkfield. Right: Creeping along the San Andreas Fault has caused offset across this road.

9. Distorted Fence across the San Andreas Fault, Melendy Ranch • These faults display a relatively constant, slow displacement called fault creep. • The continuous offset displaces sidewalks, curbs, and other cultural features along the faults. Curb offset in 1974 (above) & in 1993(below)Hayward Offset of culvert near Almaden Cienega Winerynear Hollister

10. The Carrizo Plain and the 1857 Fort Tejon Earthquake Along the relatively straight, relatively simple segment of the fault, one can view the offset streams, compressional ridges, linear valleys, and sag ponds that characterize a transform fault on land. Wallace Creek, offset by motion along the San Andreas Aerial view of the San Andreas as it crosses the Carrizo Plain

11. The 1857 Fort Tejon Earthquake San Andreas Fault • January 9, 1857, an ~M 7.8 earthquake ruptured the San Andreas Fault from Parkfield through the Big Bend segment and southeast at least to Wrightwood, a total of at least 360 kilometers. • Fort Tejon, a military outpost at the southernmost end of the Carrizo Plain was one of few population centers near the epicenter. • The ground shook for 1 to 3 minutes. • The earthquake produced as much as 8 meters of offset in the Carrizo Plain and 3 to 4 meters in the Mojave Desert. Epicenter 1857 rupture Garlock Fault Rupture area (in red) of 1857 Ft. Tejon earthquake

12. Parkfieldis located on a relatively straight section of the San Andreas fault in central California • Fault movement occurs as right lateral slip both in earthquakes and as aseismic slip, or "creep". • South of Parkfield, large earthquakes (including the 1857, M 7.8 Fort Tejon earthquake) have occurred. • From both geodetic and seismic data, currently, the southern section appears to be locked producing no small to moderate sized earthquakes. • Similarly, the section of the fault north of San Juan Bautista also has produced large earthquakes, including the M 7.5 San Francisco earthquake in 1906 and the M 6.9 Loma Prieta earthquake in 1989.

13. Most of the northern section of the fault is also currently locked, with no detectable movement and few earthquakes since 1906. • Between these locked sections, the San Andreas fault creeps (slips aseismically). • From San Juan Bautista to Parkfield, the creeping section produces numerous small (mostly M=5 and smaller) earthquakes but no large ones. • Between Parkfield and Gold Hill defines a transition zone on the SAF between the creeping and locked behavior of the fault

14. The seismicity at Parkfield: Since 1857, six similar, M~6 earthquakes have occurred on the San Andreas fault near Parkfield with apparent regularity -- one approximately every 22 years. Little is known about the first three shocks Available data suggest that all six earthquakes may have been "characteristic” The Eqs occurred with some regularity (mean repetition time of about 22 year) and may have repeatedly ruptured the same area on the fault.

15. Waveforms recorded on regional seismographs are strikingly similar for the 1922, 1934 and 1966 earthquakes, These earthquakes may have involved repeated rupture of the same area on the fault. Suggest that there may be some predictability in the occurrence of earthquakes, at least at Parkfield?? Recordings of the east-west component of motion from the 1922 earthquake (shown in black) and the 1934 and 1966 events at Parkfield (shown in red) are strikingly similar, suggesting virtually identical ruptures.

16. Do earthquakes occur completely randomly, or do they have a pattern that tends to repeat? • If they're random, there's no hope for earthquake prediction. Regular repetitions of the same rupture event, (characteristic earthquake) may be occurring at Parkfield. • This repetition was part of the basis for developing the Parkfield experiment. • Adding to the sense of repetition, similar-size foreshocks occurred 17 minutes before both the 1934 and 1966 Parkfield earthquakes. Vertical component seismograms from clustered micro-earthquakes on the San Andreas fault at Parkfield. Three types of events (numbers on left) are identified on the basis of subtle differences in the waveform.

17. 2004 Parkfield Earthquake Are these six earthquakes "characteristic" with a mean repetition time of about 22 year?

18. September 28, 2004 Parkfield Earthquake • Ruptured the same segment of the fault that broke in 1966. • 8 km depth. • Northwest rupture primarily along the San Andreas fault. • Strong shaking lasted for about 10 seconds. • This earthquake is the seventh in a series of repeating earthquakes on this stretch of the fault. • The previous events were in 1857, 1881, 1901, 1922, 1934, and 1966. M>2 aftershocks following the September 28, 2004 M6.0 earthquake

19. Cross-section showing earthquake depth along the fault within the dashed red box.

20. View across a bridge near Parkfield, from the North American Plate to the Pacific Plate. The bent rail is due to the motion of the San Andreas fault under the bridge since it was built. Red-blue 3D glasses are required.

21. Crack along the San Andreas fault near the Parkfield bridge. Both en echelon (stepping) cracks opened in tension and have right-lateral slip corresponding to motion on the San Andreas fault. View across a bridge near Parkfield, from the Pacific Plate to the North American Plate. The bent rail is due to the motion of the San Andreas fault under the bridge since it was built.

22. Peak peak accelerations and most of the peak velocities from the strong motion instruments. Data from these 54 instruments, as well as 11 GEOS instruments maintained by USGS. The additional peak velocities provide significant detail to the map of instrumental Intensity.

24. EQ Prediction The modern era of scientific earthquake predictionbegan, perhaps, in the mid- to late 1970's. In the winter of 1975, Chinese officials had ordered the evacuation of the city of Haicheng (population of about 1 million) in the Liaoning Province of northeast China, Over a period of months, changes in land elevation and ground water levels had been reported, and there were widespread accounts of peculiar animal behavior and other possible precursors to an earthquake.

25. EQ Prediction A regional increase in seismicity (later was recognized as foreshocks) had triggered a low-level alert. Subsequently, an increase in foreshock activity triggered the evacuation warning. The M7.3 earthquake struck the region days later on February 4, 1975. Physical injury and death affected only a small fraction of the total population; 2,041 people died, 27,538 were injured. It was estimated that the number of fatalities and injuries would have exceeded 150,000 if no earthquake prediction and evacuation had been made. ·  Over a period of months, changes in land elevation and ground water levels ·  Widespread accounts of peculiar animal behavior ·  Regional increase in seismicity had triggered a low-level alert. ·  Increase in foreshock activity triggered the evacuation warning.

26. EQ Prediction The optimism inspired by this success was short-lived. The following year, on July 28, 1976, a magnitude 7.6 earthquake struck the city of Tangshan, without warning. None of the precursors observed near Haicheng were observed this time. The earthquake caused an estimated 250,000 fatalities and 164,000 injured. A team of scientists from the U.S. visited laboratories in China in 1976 to investigate the Haicheng prediction. Their report concluded that the 1975 Haicheng prediction was based mainly on the pronounced foreshock sequence; other aspects of the described methodology were more difficult to assess. Lu Dongao/Xinhua

27. Seismometers ( ), borehole dilatometers ( ), creep-meters ( ), and lines of the geodetic figure monitored with two-color laser ( ) near the preparation and rupture zones of Parkfield characteristic earthquakes.

28. Lu Dongao/Xinhua Parkfield recurrence s1 represents the failure stress of the fault. Most characteristic earthquakes occur at al; the 1934 shock occurred at a2. A constant loading rate of 2.8 cm per year and a coseismic slip of 60 cm for the Parkfield earthquake sequences in 1881, 1901, 1922,1934, and 1966 are assumed.

29. Lu Dongao/Xinhua b) Series of earthquake sequences at Parkfield since 1850. The line represents the linear regression of the time of the sequence obtained without the 1934 sequence, The anticipated time of the seventh Parkfield sequence for the regression is January 1988. c) Shocks of ML greater than 4 since 1930 have tended to occur when the stress exceeded s2.

30. Parkfield Will the strain release during the next earthquake be approximately the inverse, both in amount and distribution, of the strain accumulation since the 1966 shock? The answer is crucial to the basic assumptions underlying earthquake recurrence models, such as the time-predictable and Parkfield recurrence models, which are the foundation of long-term prediction efforts. 2) Are there changes in the details of the deformation field that might permit a refined estimate of the time of the next earthquake? The answer to this question will have a major impact on efforts toward medium- and short-term prediction.

31. Parkfield Meanwhile, 1988 has come and gone at Parkfield with no earthquake, while two other damaging earthquakes have struck in California, both on little-known faults in the south. The error in the Parkfield timetable has been explained in two ways. Jim Savage ( USGS) has argued that the original premise was fallacious, since it only considered a single, non-unique recurrence scenario. Or, Steve Miller of UTH Zurich has suggested that a nearby thrust earthquake in Coalinga in 1983 reset the clock at Parkfield. Fault trace at Carr Hill, south of Parkfield on the west side of the San Andreas Fault.

32. A sliding scale of earthquake 'prediction’ Time-independent hazard. We assume that earthquakes are a random (Poisson) process in time, and use past locations of earthquakes, active faults, geological recurrence times and/or fault slip rates from plate tectonic or satellite data to constrain the future long-term seismic hazard. We then calculate the likely occurrence of ground-shaking from a combination of source magnitude probability with path and site effects, and include a calculation of the associated errors. Such calculations can also be used in building design and planning of land use, and for the estimation of earthquake insurance. Two-color laser geodimeter at Car Hill, Parkfield, CA. National Geographic Society.

33. Time-dependent hazard. Here we accept a degree of predictability in the process, in that the seismic hazard varies with time. We might include linear theories, where the hazard increases after the last previous event, or the idea of a 'characteristic earthquake' with a relatively similar magnitude, location and approximate repeat time predicted from the geological dating of previous events. Surprisingly, the tendency of earthquakes to cluster in space and time include the possibility of a seismic hazard that actually decreases with time. This would allow the refinement of hazard to include the time and duration of a building's use as a variable in calculating the seismic risk. Doug Myren installing a borehole strainmeter (dilatometer) at Joaquin Canyon, near Parkfield, CA. (1987).

34. Earthquake forecasting. Try to predict some of the features of an impending earthquake, usually on the basis of the observation of a precursory signal. The prediction would still be probabilistic, in the sense that the precise magnitude, time and location might not be given precisely or reliably, There is some physical connection above the level of chance between the observation of a precursor and the subsequent event. Forecasting would also have to include a precise statement of the probabilities and errors involved Must demonstrate more predictability than the clustering referred to in time-dependent hazard. Portable Two-Color EDM set up at Middle Mountain.

35. Earthquake forecasting con’t. The practical utility of this would be to enable the relevant authorities to prepare for an impending event on a timescale of months to weeks. Practical difficulties include identifying reliable, unambiguous precursors, and the acceptance of an inherent proportion of missed events or false alarms, involving evacuation for up to several months at a time, resulting in a loss of public confidence. GPS at Carr Hill, Parkfield, CA.

36. Deterministic prediction. Earthquakes are inherently predictable. We can reliably know in advance their location (latitude, longitude and depth), magnitude, and time of occurrence, all within narrow limits (again above the level of chance), so that a planned evacuation. Time-independent hazard has now been standard practice for three decades, although new information from geological and satellite data is increasingly being used as a constraint. We cannot specify time-dependent hazard well at all: in fact, we have two antithetical paradigms. Clustering models predict that earthquake probability is enhanced immediately after a large event. Schematic cross section of the San Andreas Fault Zone at Parkfield, showing the planned drill hole for the San Andreas Fault Observatory at Depth (SAFOD) and the pilot hole drilled in 2002.

37. Predicting earthquakes requires an understanding of the underlying physics, which calls for novel multidisciplinary approaches at a level never yet undertaken. We still have very limited precise quantitative measurements of the many parameters involved. The physical phenomena underlying earthquakes are much more intricate and interwoven and we do not have a fundamental equation for the crustal organization. Video camera looking along San Andreas fault at Parkfield, CA.

38. The 1983 Coalinga and Nuñez Eqs -- Parkfield earthquake prediction Stress changes caused by two large earthquakes northeast of the San Andreas fault in 1983 increased stress on the creeping section of the fault, causing the rate of small shocks to rise for about 18 months. The shocks also decreased stress on the locked Parkfield segment Triggered surface creep and seismicity rates to drop at Parkfield segment for >6 yrs. The 1983 EQ’s temporally reduced the 10-year probability of a M~6 Parkfield earthquake. Shear stress transferred by the 2 May 1983 M6.5 Coalinga & 11 June to 22 July M6.0 Nuñez earthquakes.

39. The 2004 Parkfield earthquake • Lack of obvious precursors • Presumption of regularity in earthquake cycles • Departures from steady-state strain accumulation (think about this?) • Reliable short-term earthquake prediction still is not achievable.

40. Changes of aseismic slip rate in the interseismic period (possible increase) • Slip was smaller in 1922 EQ, because of an assumed larger fault area. • Strength or loading rate variable • Stress changes along fault - stress triggering • Observed sequence is consistent that earthquakes occur according to a Poisson, rather than quasi-periodic, model.

41. Two Big Questions: *Where will earthquakes start? * Where will earthquakes stop? Possible Answers: Both initiation and termination are likely caused by *Fault Zone Rheology Friction, Deformation Styles *Fault Zone Stress Conditions Tectonics, Stress Triggers/Shadows, Pore-pressure state *Fault Zone Geometry Fault Continuities and Discontinuities) It is probably best to assume that earthquakes can start anywhere (on faults). Large earthquakes can be stopped by 1) Encountering large creeping sections of a fault 2) A Stress shadow from a recent large earthquake on the same fault 3) Big changes in fault geometry. (e.g., inter-fault distances of >5 km) March 2006 WGCEP Workshop

42. Two Big Questions: *Where will earthquakes start? * Where will earthquakes stop? Possible Answers: Large earthquakes tend to occur as similar-size characteristic’ events on fixed segments of a fault and that these segments are identifiable from geologic and geophysical data. Remains central to fault-based Probabilistic Seismic Hazard Analysis (PSHA). March 2006 WGCEP Workshop

43. The sequence of earthquakes at Parkfield since 1857 has long been • considered a prime example of the recurrence of a characteristic • earthquakes. • Two classes of characteristic earthquakes. • Events have the same faulting mechanism and magnitude, and occur on the same fault segement • This class of characteristic behavior is most appropriate for long- • term forecasting of earthquakes and is often inferred from paleo- • seismic investigations. • 2) Events also have the same epicenter and rupture direction. • If the second class were further constrained to have the same rupture time history and distribution of slip, then this class of recurrent behavior would imply low variability in the distribution of strong ground shaking among the recurrences of characteristic events. March 2006 WGCEP Workshop

44. Initial thoughts The 1934, 1966 and 2004 Parkfield earthquakes are remarkably similar in size and location of rupture, although not in epicenter or rupture propagation direction. The aftershocks of the 1966 and 2004 earthquakes delineate many of the same fault structures. Thus, the Parkfield earthquakes are consistent with the first class of characteristic earthquake behavior. Issues with predication The variability in the spatial distribution of slip for the last three events and the different direction of rupture propagation in the 2004 event invalidates the application of the second class of characteristic behavior to the Parkfield earthquakes. March 2006 WGCEP Workshop

45. End-member models of earthquake recurrence Time-predictable model The time between successive events is proportional to the slip of the prior event Slip-predictable model The size of an earthquake is proportional to the time since the prior event. Upshot at Parkfield Neither of these models is compatible with the sequence of Parkfield earthquake ruptures. Various forms of fault interaction might explain the variation in recurrence intervals of the earthquake.

46. Implications for the future • The magnitude and rupture extent of the 2004 Parkfield earthquake were correctly anticipated • The time of occurrence clearly was not correctly anticipated. • Suggests that long-term earthquake forecasts require models that include higher degrees.

47. Implications for the future • Although the 2004 Parkfield earthquake was ideally located within a • dense monitoring network specifically designed to detect foreshocks • and other possible short-term precursors, no significant signals were • detected. • The absence of clear precursory sets stringent bounds on the processes that preceded this earthquake. • Attempts to detect short-term precursory strain changes near several • other recent Mw 5.3–7.3 earthquakes in California and Japan have • also failed. • These experiences demonstrate that reliable short-term earthquake prediction (up to a few weeks in advance) will be very difficult at best.

48. Introduction to Earthquake Cycle and Geodetic observations • Modeled as elastic lithosphere overlying a viscoelastic asthenosphere. • Displacement on a single fault that slip periodically in large earthquakes. • The fault that cuts through entire elastic lithosphere. • The lower part of the fault creeps at continuously at a slip rate equal to plate rate. Flow rate constant in asthenosphere. • The stresses on the fault are generated by far field load (tectonic motions) and time-dependent loading of the lithosphere due to viscoelastic flow in the asthenosphere.

49. Introduction to Earthquake Cycle and Geodetic observations Stage 1 Interseismic deformation. Far field deformation present on the Earth's surface at about a fault depth away from the locked zone

50. Introduction to Earthquake Cycle and Geodetic observations Stage 2 Coseismic deformation, showing discrete slip along fault, note far field base line has elastically recovered along a horizontal datum