Three-dimensional passive seismic waveform imaging around the SAFOD site, California, using the generalized Radon transform (original) (raw)
Related papers
GEOPHYSICS, 1988
Shot gathers from the Parkfield, California, deep crustal seismic reflection line, recorded in 1977 by COCORP, reveal coherent events having horizontal to reverse moveouts. These events were migrated using a multioffset three-dimensional Kirchhoff summation method. This method is a ray-equation back projection inversion of the acoustic wave field. which is valid under the Born, WKBJ, and far-field assumptions. Migration of full-wave acoustic synthetics, having the same limitations in geometric coverage as the COCORP survey, demonstrates the utility of the imaging process. The images obtained from back projection of the survey data suggest that the Gold Hill fault carries ultramafic rocks from the surface to 3 km depth at a dip greater than 45 degrees. where it joins the San Andreas fault, which may cut through more homogeneous materials at shallow depths. To the southwest, a 2 km Tertiary sedimentary section appears to terminate against a nearvertical fault. The zone between this fault and the San Andreas may be floored at 3 km by flat-lying ultramatics. Lateral velocity inhomogeneities are not accounted for in the migration but, in this case, do not seriously hinder the reconstruction of reflectors.
Open-File Report, 1999
The geology within the adjacent San Bernardino Mountains consists largely of pre-Cambrian metamorphic and igneous rocks (gneisses, schists, and Mesozoic granites; Jennings et al., 1977). Within San Gorgonio Pass, Pliocene sandstones, gravels, and clays are overlain by Quaternary alluvium (Jennings et al., 1977). Within the study area, Boyle Engineering Co. (1992) further categorized the upper 300 m of the Quaternary and Pliocene units as the San Timoteo Formation, the Old Red gravel, older alluvium, and recent alluvium. For purposes of discussion in the report, we will use the Boyle Engineering categorization for the shallow-depth lithology. Along most of the seismic profiles, the upper 20 m of the Quaternary Alluvium unit consists of poorly sorted, unconsolidated gravel, sand, cobbles, and boulders. Underlying the Quaternary alluvium unit is the older alluvium unit, which consists of similar materials that are more consolidated. Beneath the older alluvium unit, the Old Red gravel unit consists of reddish-brown, poorly sorted, coarse gravel, sands, and is about 30 m thick in the Cherry Valley area. The San Timoteo Formation (~75 to 100 m below land surface) is the oldest geologic unit encountered in the boreholes at the existing recharge site, and it consists of poorly sorted to-well-sorted, partly consolidated, fine-to-coarse sand, gravel and cobbles with thin clay layers (Boyle Engineering Co., 1992). Tectonically, the Cherry Valley-Beaumont area is complex. The study area lies atop an alluvial fan that has been deposited on the southwest side of the San Bernardino Mountains. Major strands of the San Andreas fault trend through the San Bernardino Mountains and within the immediate study area. Strike-slip, thrust, and normal faults have been mapped in the vicinity of our seismic profiles (Figure 1b). Near the northern end of our seismic profiles, the Banning strand of the San Andreas fault has been mapped and consists of both thrust and strike-slip components that vary greatly in strike (Figure 1). Further south along the seismic profile, Matti et al. (1992) infer near-surface faults that are dominantly north-south-oriented and have normal components of motion. This tectonic complexity is caused largely by a change in the strike of the San Andreas fault system from a northwest orientation south of San Gorgonio Pass to one that is predominantly east-west within San Gorgonio Pass. Seismic Survey Data Acquisition In August 1998, the US Geological Survey acquired three high-resolution seismic reflection profiles along Noble Creek in Cherry Valley (Fig 1). These profiles are southward continuations of seismic reflection/refraction profiles acquired further north along Noble and Little San Gorgonio Creeks in July-August, 1997 (Catchings et al., 1999). The seismic profiles acquired in the present study (labeled CV-5, CV-6, and CV-7 in Figure 1a) range in length from about 715 m to about 1609 m (see Table 1). All three profiles had a northeast-southwest orientation.
2021
Reflection seismic imaging usually suffers from a loss of resolution and contrast because of the fluctuations of the wave velocities in the Earth's crust. In the literature, phase distortion issues are generally circumvented by means of a background wave velocity model. However, it requires a prior tomography of the wave velocity distribution in the medium, which is often not possible, especially in depth. In this paper, a matrix approach of seismic imaging is developed to retrieve a three-dimensional image of the subsoil, despite a rough knowledge of the background wave velocity. To do so, passive noise cross-correlations between geophones of a seismic array are investigated under a matrix formalism. More precisely, the detrimental effect of wave velocity fluctuations on imaging is overcome by introducing a novel mathematical object: The distortion matrix. This operator essentially connects any virtual source inside the medium with the distortion that a wavefront, emitted from ...
Journal of Structural Geology, 2002
Aftershocks of the 1994 Northridge earthquake (M 6.8) allow us to image the structure beneath the San Fernando Valley in northwestern Los Angeles in three dimensions. We combine aftershocks and geological data to build an image of the three-dimensional (3-D) geometry of the previously unrecognized, north-vergent Northridge blind thrust to a depth of 21 km. The most striking feature of the imaged fault is megacorrugations oriented parallel to the mean aftershock slip vector, with most of the 1994 slip con®ned to west of the largest corrugation. We also image the partially overlying south-vergent San Fernando thrust, which broke to the surface in a complex rupture in 1971 (M 7.1). Both thrusts produce fault-related folding because of either fault propagation or fault bends; however, this deeper folding is masked by overlying complex deformation in the cover, which is one reason why the Northridge thrust was not identi®ed until it ruptured in 1994. We use trishear fold modeling based on our 3-D fault geometry to evaluate possible folding due to slip on the Northridge thrust as well as its interaction with the overlapping San Fernando thrust and with shallow structures in the cover. This example illustrates the importance of earthquake data to structural geology and the value of its 3-D integration with surface and near-surface geological data.
A return to passive seismic imaging
Rekindling the passive seismic imaging effort at Stanford, I have acquired grants with Simon Klemperer of the Stanford Crustal Research Group from both the Petroleum Research Fund and the National Science Foundation to pursue two-and three-dimensional imaging efforts of the subsurface in a passive listening methodology. Utilizing the outstanding SEP hardware and software infrastructure and expertise, I have begun to build the resources necessary to manipulate the massive datasets toward producing an image. Efforts to acquire several existing datasets that seem to fit the requirements of this method are presently underway, while 180 Gbytes of the Santa Clara Valley Seismic Experiment from 1998 arrived in house on the first of March.
Crustal imaging in southern California using earthquake sequences
Tectonophysics, 1998
An inexpensive means to further understand the geometry of active faults in southern California arises from the use of aftershock recordings to image crustal structures. The advent of regional seismic networks that record digital seismograms from hundreds of ...
Imaging of earthquake sources in Long Valley Caldera, California
Bulletin of the Seismological Society of America
A finite difference technique by which an earthquake wave field recorded at the Earth's surface could be extrapolated backward in time to produce an image of the source was presented by . The resulting image is dynamic and reveals the temporal and spatial configuration of the acoustic equivalent of the source. The method was successfully tested on synthetic data, but no real earthquake data satisfying the prerequisites for processing were available in 1982. The data must be recorded close to the source and must be spatially dense. In January of 1983, a unique data set was recorded by the U.S. Geological Survey within Long Valley Caldera in eastern California. Three events were chosen from the aftershock sequence. Preprocessing of the data for each event includes construction of a true amplitude section, filtering, and extrapolation to produce unaliased, equally spaced observations. Extrapolation of these data through a previously determined velocity structure produces coherent images in which both the source location and radiation pattern are visible. The images are also consistent with previously determined focal mechanisms. The results demonstrate the feasibility of imaging real earthquake sources.
Journal of Geophysical Research, 1999
We apply inversion methods to first arriving P waves from explosive source seismic data collected along line 1 of the Los Angeles Region Seismic Experiment (LARSE), extending northeastward from Seal Beach, California, to the Mojave Desert, in order to determine a seismic model of the upper crust along the profile. We use resolution information to quantify the extent of blurring in the LARSE images and to smooth a damped least squares (DLS) image by postinversion filtering (PIF). Most of the original data fit is preserved while minimizing model artifacts. We compare DLS, PIF, and smoothing constraint inversion images using both real and synthetic data. A preferred PIF image includes larger-scale features in the smoothing constraint inversion image and finer-scale features in the DLS inversion image that are consistent with geologic information. We interpret principal model features in terms of geology, including faulting. The maximum depth of low-velocity sedimentary and volcanic rocks in the Los Angeles basin is 8-9 km and in the San Gabriel Valley is 4.5-5 km. A horst-like uplift of basement rocks occurs between these basins. The northeastern boundary of the San Gabriel Valley is imaged as a tabular, moderately north dipping low-velocity zone that projects to the surface at the southernmost trace of the Sierra Madre fault system. In the central and southern San Gabriel Mountains, velocitydepth profiles are consistent with intermediate-velocity mylonites overlying lower-velocity Pelona Schist along a shallowly southwest dipping Vincent thrust fault. Tomography does not provide a definitive dip for the San Andreas fault but, combined with other LARSE results, is consistent with a vertical to steep northeast dip. 1Department Specific imaging targets included the bottoms of the Los Angeles and San Gabriel Valley sedimentary basins, the geometries of basin-bounding faults, including the Whittier and Sierra Madre fault zones, and the deep structure of the San Gabriel Mountains, beneath which at least two major fault zones converge, the San Andreas and Sierra Madre fault zones.
GEOPHYSICS, 2006
Passive seismic imaging is the process of synthesizing the wealth of subsurface information available from reflection seismic experiments by recording ambient sound with an array of geophones distributed at the surface. Cross-correlating the traces of such a passive experiment can synthesize data that is immediately useful for analysis by the various techniques that have been developed for the manipulation of reflection seismic data. With a correlation-based imaging condition, wave-equation shot-profile depth migration can use raw transmission wavefields as input to produce a subsurface image. For passively acquired data, migration is even more important than for active data because the source wavefields are likely weak and complex which leads to a low signal-to-noise ratio. Fourier analysis of correlating long field records shows that aliasing of the wavefields from distinct shots is unavoidable. While this reduces the order of computations for correlation by the length of the original trace, the aliasing produces an output volume that may not be substantially more useful than the raw data due to the introduction of cross talk between multiple sources. Direct migration of raw field data can still produce an accurate image even when the transmission wavefields from individual sources are not separated. I illustrate the method with images from a shallow passive investigation targeting a buried hollow pipe and the water table reflection. The images show a strong anomaly at the 1 m depth of the pipe and faint events that could be the water table around 3 m. The images are not so clear as to be irrefutable. A number of deficiencies in the survey design and execution are identified for future efforts.