U.S.-Japan Quake Prediction Research

For the seventh time since 1964, a seminar on earthquake prediction has been convened under the U.S.-Japan Cooperation in Science Program. The purpose of the seminar was to provide an opportunity for researchers from the two countries to share recent progress and future plans in the continuing effort to develop the scientific basis for predicting earthquakes and practical means for implementing prediction technology as it emerges. Thirty-six contributors, 15 from Japan and 21 from the U.S., met in Morro Bay, Calif.September 12–14. The following day they traveled to nearby sections of the San Andreas fault, including the site of the Parkfield prediction experiment. The conveners of the seminar were Hiroo Kanamori, Seismological Laboratory, California Institute of Technology (Caltech), for the U.S., and Takeshi Mikumo, Disaster Prevention Research Institute, Kyoto University, for Japan. Funding for the participants came from the U.S. National Science Foundation and the Japan Society for the Promotion of Science, supplemented by other agencies in both countries

Seventh U.S.-Japan Earthquake Prediction Research Seminar: Use of Real-Time Earthquake Information for Hazard Warning

For the seventh time since 1964, a seminar on earthquake prediction has been convened under the U.S.-Japan Cooperation in Science Program. The purpose of the seminar was to provide an opportunity for researchers from the two countries to share recent progress and future plans in the continuing effort to develop the scientific basis for predicting earthquakes and practical means for implementing prediction technology as it emerges. Thirty-six contributors, 15 from Japan and 21 from the U.S., met in Morro Bay, California, September 12-14. The following day they traveled to nearby sections of the San Andreas fault, including the site of the Parkfield prediction experiment. The conveners of the seminar were Hiroo Kanamori, Seismological Laboratory, Caltech, for the U.S., and Takeshi Mikumo, Disaster Prevention Research Institute, Kyoto University, for Japan. Funding for the participants came from the U.S. National Science Foundation and the Japan Society for the Promotion of Science, supplemented by other agencies in both countries

Nonvolcanic tremor observed in the Mexican subduction zone

Nonvolcanic tremor (NVT) activity is revealed as episodes of higher spectral amplitude at 1–8 Hz in daily spectrograms from the continuous seismological records in Guerrero, Mexico. The analyzed data cover a period of 2001–2007 when in 2001–2002 a large slow slip event (SSE) had occurred in the Guerrero-Oaxaca region, and then a new large SSE occurred in 2006. The tremor burst is dominated by S-waves. More than 100 strong NVT bursts were recorded in the narrow band of ~40 × 150 km^2 to the south of Iguala City and parallel to the coastline. Depths of NVT hypocenters are mostly scattered in the continental crust between 5 and 40 km depth. Tremor activity is higher during the 2001–2002 and 2006 SSE compared with that for the “quiet” period of 2003–2005. While resistivity pattern in Guerrero does not correlate directly with the NVT distribution, gravity and magnetic anomaly modeling favors a hypothesis that the NVT is apparently related to the dehydration and serpentinization processes

Dynamic fault rupture processes of moderate-size earthquakes inferred from the results of kinematic waveform inversion

Several attempts have been made recently to infer the dynamic rupture processes of moderate-size earthquakes from kinematic waveform inversion and dynamic crack inversion. These studies have revealed a quite heterogeneous distribution of dynamic stress drop and relative fault strength over the fault for most earthquakes. In two strike-slip California earthquakes, negative stress drop has been identified in a shallow section of the fault, suggesting the possible existence of a zone of velocity-strengthening frictions. The dynamic models yielded quite short rise times comparable to those inferred from kinematic modelling of observed waveforms. The short slip durations for these earthquakes may probably be attributed to shorter length scale of fault segmentation due to the heterogeneities of shear stress and fault strength

A consideration on generation mechanism of local earthquakes

The mechanism of occurrence of local earthquakes generated in Wakayama Disrict was studies from the "push-pull" pattern of initial motions and the amplitude distributions of the P- and S-waves. It may safety be explainable to be of a conical type rather than quadrant one. A consideration on the former type of mechanism may suggest an azimuthal difference in the dimension of focal region

Atmospheric pressure waves and tectonic deformation associated with the Alaskan earthquake of March 28

Atmospheric pressure disturbances with periods as long as 14 min have been recorded by sensitive microbarographs at five stations along the Pacific coast and at a station in Alaska after the great Alaskan earthquake of March 28, 1964. The phase and group velocities of the disturbances are consistent with those so far observed in atmospheric nuclear explosions and with theoretical dispersion curves for acoustic-gravity waves. These velocities and field observation of the tectonic deformations in the epicentral region suggest that the pressure disturbances might have been caused by the rapid vertical ground displacement at the source area. Theoretical barograms appropriate to the Berkeley station have been constructed on the basis of reasonable estimates for the source dimension, the amount of uplift and subsidence, and the time rate of the displacement, taking the atmospheric and instrumental responses into account. Agreement between general features of the observed and theoretical barograms appears sufficient to support the above generation hypothesis, suggesting a possible range for the time rate of the surface tectonic deformation

Faulting process of the San Fernando earthquake of February 9, 1971 inferred from static and dynamic near-field displacements

The faulting process of the San Fernando earthquake of February 9, 1971 has been investigated using the following seismic and geodetic data: vertical and horizontal displacements, strain and tilt changes, dynamic ground motions in the near-field, focal mechanism, spatial distribution of aftershocks and features of surface fault breaks. A synthetic study suggests that the earthquake was caused by thrust faulting with a slip of 233° to 244° over a fault plane with dimensions 19 by 14 km, dip 50° to 52° and strike N64° to 70°W, which ruptures the ground surface over a distance of about 12 km. The fracture initiating at the hypocenter of the main shock seems to have propagated radially over the fault plane with a velocity about 2.5 km/sec. A small dislocation less than 30 cm at initiation probably increased rapidly during propagation and reached 3.5 to 4 m at the ground surface. A pronounced uplift and small subsidence of the ground north and south of the fault traces, and the overall pattern of the observed vertical and horizontal displacements can be explained well by the above model, but the recorded strain and tilt offsets are not always consistent with theoretical predictions. The wave forms and amplitudes for some of the integrated ground displacements from accelerograms at the Pacoima Dam and Pasadena are in fairly close agreement with those of the computed displacements. The seismic moment and stress drop of this earthquake were found to be 1.1 × 1026 dyne·cm and 40 to 65 bars, respectively

A possible rupture process of slow earthquakes on a frictional fault

A possible mechanism for the occurrence of slow earthquakes is investigated by calculating numerical solutions for the dynamical rupture process on a quasi-three-dimensional fault with heterogeneous frictional strengths. Experimental friction laws for the dependence of sliding frictional stress on slip velocity, which are based on the cohesive properties of fault asperities, are taken into considerations. It is found that the applied stress does not drop very rapidly with time and the rupture velocity remarkably decreases as the dependence on slip-velocity becomes smaller. These deceleration effects for the rupture propagation are greatly enhanced with increasing heterogeneities in the distribution of frictional strength and as the initial shear stress has lower levels with respect to the average strength. For these cases, the growth of rupture is extremely slow in a nucleus region with the dimension as large as 10 times the initial rupture length, and gains a terminal velocity dependent on the above factors. The displacement-time function becomes noticeably extended in these cases, and indicates a stick—slip-like phenomena in the extended time interval for a strongly heterogeneous fault. It seems that these results could explain the characteristic features of slow earthquakes