Search USGS⌕ Search

Geology topics

C. G. Bufe

Publications and source records attributed to C. G. Bufe.

At least 19 recordsLinked to original sources
USGS2012

Predictive modeling of the seismic cycle of the greater San Francisco Bay region

The seismic cycle for the San Francisco Bay region is synthesized by a model combining the pre- and post-1906 seismic histories. The long-term acceleration of seismic release (seismic moment, Benioff strain release, or event count) in the seismic cycle and the shorter-term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique, called a time-to-failure analysis, in which rate of seismic release is proportional to an inverse power of the remainng time to failure. The exponent of time to failure in the accelerating sequences appears to be scale invariant, and the length of the full cycle is estimated at 269±50 yr. The 1989 Loma Prieta earthquake should have been predictable with an uncertainty of two years in time and 0.5 in magnitude, although the specific location (at Loma Prieta) was not predictable by this technique. If the model is correct, the San Francisco Bay region should be entering a relatively long (20-50 yr) period of seismic quiescence above magnitude 6.

California↗
USGS2005

Evidence for a global seismic-moment release sequence

Temporal clustering of the larger earthquakes (foreshock-mainshock-aftershock) followed by relative quiescence (stress shadow) are characteristic of seismic cycles along plate boundaries. A global seismic-moment release history, based on a little more than 100 years of instrumental earthquake data in an extended version of the catalog of Pacheco and Sykes (1992), illustrates similar behavior for Earth as a whole. Although the largest earthquakes have occurred in the circum-Pacific region, an analysis of moment release in the hemisphere antipodal to the Pacific plate shows a very similar pattern. Monte Carlo simulations confirm that the global temporal clustering of great shallow earthquakes during 1952-1964 at M ??? 9.0 is highly significant (4% random probability) as is the clustering of the events of M ??? 8.6 (0.2% random probability) during 1950-1965. We have extended the Pacheco and Sykes (1992) catalog from 1989 through 2001 using Harvard moment centroid data. Immediately after the 1950-1965 cluster, significant quiescence at and above M 8.4 begins and continues until 2001 (0.5% random probability). In alternative catalogs derived by correcting for possible random errors in magnitude estimates in the extended Pacheco-Sykes catalog, the clustering of M ??? 9 persists at a significant level. These observations indicate that, for great earthquakes, Earth behaves as a coherent seismotectonic system. A very-large-scale mechanism for global earthquake triggering and/or stress transfer is implied. There are several candidates, but so far only viscoelastic relaxation has been modeled on a global scale.

Bulletin of the Seismological Society of America↗
USGS2004

Stress transfer to the Denali and other regional faults from the M 9.2 Alaska earthquake of 1964

Stress transfer from the great 1964 Prince William Sound earthquake is modeled on the Denali fault, including the Denali-Totschunda fault segments that ruptured in 2002, and on other regional fault systems where M 7.5 and larger earthquakes have occurred since 1900. The results indicate that analysis of Coulomb stress transfer from the dominant earthquake in a region is a potentially powerful tool in assessing time-varying earthquake hazard. Modeled Coulomb stress increases on the northern Denali and Totschunda faults from the great 1964 earthquake coincide with zones that ruptured in the 2002 Denali fault earthquake, although stress on the Susitna Glacier thrust plane, where the 2002 event initiated, was decreased. A southeasterlytrending Coulomb stress transect along the right-lateral Totschunda-Fairweather-Queen Charlotte trend shows stress transfer from the 1964 event advancing slip on the Totschunda, Fairweather, and Queen Charlotte segments, including the southern Fairweather segment that ruptured in 1972. Stress transfer retarding right-lateral strike slip was observed from the southern part of the Totschunda fault to the northern end of the Fairweather fault (1958 rupture). This region encompasses a gap with shallow thrust faulting but with little evidence of strike-slip faulting connecting the segments to the northwest and southeast. Stress transfer toward failure was computed on the north-south trending right-lateral strike-slip faults in the Gulf of Alaska that ruptured in 1987 and 1988, with inhibitory stress changes at the northern end of the northernmost (1987) rupture. The northern Denali and Totschunda faults, including the zones that ruptured in the 2002 earthquakes, follow very closely (within 3%), for about 90° , an arc of a circle of radius 375 km. The center of this circle is within a few kilometers of the intersection at depth of the Patton Bay fault with the Alaskan megathrust. This inferred asperity edge may be the pole of counterclockwise rotation of the block south of the Denali fault. These observations suggest that the asperity and its recurrent rupture in great earthquakes as in 1964 may have influenced the tectonics of the region during the later stages of evolution of the Denali strike-slip fault system.

Alaska↗
USGS2003

Moment-tensor solutions estimated using optimal filter theory: Global seismicity, 2001

This paper is the 12th in a series published yearly containing moment-tensor solutions computed at the US Geological Survey using an algorithm based on the theory of optimal filter design ( Sipkin, 1982 and Sipkin, 1986b ). An inversion has been attempted for all earthquakes with a magnitude, m b or M S , of 5.5 or greater. Previous listings include solutions for earthquakes that occurred from 1981 to 2000 ( Sipkin, 1986b ; Sipkin and Needham, 1989 , Sipkin and Needham, 1991 , Sipkin and Needham, 1992 , Sipkin and Needham, 1993 , Sipkin and Needham, 1994a and Sipkin and Needham, 1994b ; Sipkin and Zirbes, 1996 and Sipkin and Zirbes, 1997 ; Sipkin et al., 1998 , Sipkin et al., 1999 , Sipkin et al., 2000a , Sipkin et al., 2000b and Sipkin et al., 2002 ). The entire USGS moment-tensor catalog can be obtained via anonymous FTP at ftp://ghtftp.cr.usgs.gov . After logging on, change directory to “momten”. This directory contains two compressed ASCII files that contain the finalized solutions, “mt.lis.Z” and “fmech.lis.Z”. “mt.lis.Z” contains the elements of the moment tensors along with detailed event information; “fmech.lis.Z” contains the decompositions into the principal axes and best double-couples. The fast moment-tensor solutions for more recent events that have not yet been finalized and added to the catalog, are gathered by month in the files “jan01.lis.Z”, etc. “fmech.doc.Z” describes the various fields.

Physics of the Earth and Planetary Interiors↗
USGS1996

The cyclic and fractal seismic series preceding an mb 4.8 earthquake on 1980 February 14 near the Virgin Islands

Seismic activity in the 10 months preceding the 1980 February 14, m b 4.8 earthquake in the Virgin Islands, reported on by Frankel in 1982, consisted of four principal cycles. Each cycle began with a relatively large event or series of closely spaced events, and the duration of the cycles progressively shortened by a factor of about 3/4. Had this regular shortening of the cycles been recognized prior to the earthquake, the time of the next episode of seismicity (the main shock) might have been closely estimated 41 days in advance. That this event could be much larger than the previous events is indicated from time-to-failure analysis of the accelerating rise in released seismic energy, using a non-linear time- and slip-predictable foreshock model. Examination of the timing of all events in the sequence shows an even higher degree of order. Rates of seismicity, measured by consecutive interevent times, when plotted on an iteration diagram of a rate versus the succeeding rate, form a triangular circulating trajectory. The trajectory becomes an ascending helix if extended in a third dimension, time. This construction reveals additional and precise relations among the time intervals between times of relatively high or relatively low rates of seismic activity, including period halving and doubling. The set of 666 time intervals between all possible pairs of the 37 recorded events appears to be a fractal; the set of time points that define the intervals has a finite, non-integer correlation dimension of 0.70. In contrast, the average correlation dimension of 50 random sequences of 37 events is significantly higher, close to 1.0. In a similar analysis, the set of distances between pairs of epicentres has a fractal correlation dimension of 1.52. Well-defined cycles, numerous precise ratios among time intervals, and a non-random temporal fractal dimension suggest that the seismic series is not a random process, but rather the product of a deterministic dynamic system.

Geophysical Journal International↗
USGS1994

Seismicity trends and potential for large earthquakes in the Alaska-Aleutian region

The high likelihood of a gap-filling thrust earthquake in the Alaska subduction zone within this decade is indicated by two independent methods: analysis of historic earthquake recurrence data and time-to-failure analysis applied to recent decades of instrumental data. Recent (May 1993) earthquake activity in the Shumagin Islands gap is consistent with previous projections of increases in seismic release, indicating that this segment, along with the Alaska Peninsula segment, is approaching failure. Based on this pattern of accelerating seismic release, we project the occurrence of one or more M???7.3 earthquakes in the Shumagin-Alaska Peninsula region during 1994-1996. Different segments of the Alaska-Aleutian seismic zone behave differently in the decade or two preceding great earthquakes, some showing acceleration of seismic release (type "A" zones), while others show deceleration (type "D" zones). The largest Alaska-Aleutian earthquakes-in 1957, 1964, and 1965-originated in zones that exhibit type D behavior. Type A zones currently showing accelerating release are the Shumagin, Alaska Peninsula, Delarof, and Kommandorski segments. Time-to-failure analysis suggests that the large earthquakes could occur in these latter zones within the next few years. ?? 1994 Birkha??user Verlag.

Pure and Applied Geophysics PAGEOPH↗
USGS1988

The 1987 Whittier Narrows earthquake in the Los Angeles metropolitan area, California

The Whittier Narrows earthquake sequence (local magnitude, M L = 5.9), which caused over 358-million dollars damage, indicates that assessments of earthquake hazards in the Los Angeles metropolitan area may be underestimated. The sequence ruptured a previously unidentified thrust fault that may be part of a large system of thrust faults that extends across the entire east-west length of the northern margin of the Los Angeles basin. Peak horizontal accelerations from the main shock, which were measured at ground level and in structures, were as high as 0.6 g (where g is the acceleration of gravity at sea level) within 50 kilometers of the epicenter. The distribution of the modified Mercalli intensity VII reflects a broad north-south elongated zone of damage that is approximately centered on the main shock epicenter.

California↗
USGS1979

Fault-crossing P delays, epicentral biasing, and fault behavior in central California

The P delays across the San Andreas fault zone in central California have been determined from travel-time differences at station pairs spanning the fault, using off-fault local earthquake or quarry blast sources. Systematic delays as large as 0.4 sec have been observed for paths crossing the fault at depths of 5-10 km. These delays can account for the apparent deviation of epicenters from the mapped fault trace. The largest delays occur along the San Andreas fault between San Juan Bautista and Bear Valley and Between Bitterwater Valley and Parkfield. Spatial variations in fault behavior correlate with the magnitude of the fault-crossing P delay. The delay decreases to the northwest of San Juan Bautista across the "locked" section of the San Andreas fault and also decreases to the southeast approaching Parkfield. Where the delay is large, seismicity is relatively high and the fault is creeping.

California↗
USGS1978

Seismic monitoring at the Geysers geothermal field, California

Two distinct clusters of microearthquakes have been identified at The Geysers, possibly relating to two independent pressure sinks resulting from steam production described by Lipman, and others (1977). Unlike earthquakes in the Maacama-Rodgers Creek fault zone to the south and west, earthquakes at The Geysers are confined to depths of less than 5 km. The present level of seismicity at The Geysers appears to be higher than the preproduction level and is higher and more continuous than the seismicity in the surrounding region. Earthquakes in the steam production zone at The Geysers resemble earthquakes in the surrounding region with regard to focal plane solutions, source characteristics and magnitude distribution (b slope). Subtle differences in earthquake characteristics may be resolved by analysis of more extensive data now being gathered in the region.

Open-File Report↗