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Larry A. Beyer

Publications and source records attributed to Larry A. Beyer.

12 recordsLinked to original sources
USGS2009

Post-Miocene Right Separation on the San Gabriel and Vasquez Creek Faults, with Supporting Chronostratigraphy, Western San Gabriel Mountains, California

The right lateral San Gabriel Fault Zone in southern California extends from the northwestern corner of the Ridge Basin southeastward to the eastern end of the San Gabriel Mountains. It bifurcates to the southeast in the northwestern San Gabriel Mountains. The northern and older branch curves eastward in the range interior. The southern younger branch, the Vasquez Creek Fault, curves southeastward to merge with the Sierra Madre Fault Zone, which separates the San Gabriel Mountains from the northern Los Angeles Basin margin. An isolated exposure of partly macrofossiliferous nearshore shallow-marine sandstone, designated the Gold Canyon beds, is part of the southwest wall of the fault zone 5.5 km northwest of the bifurcation. These beds contain multiple subordinate breccia-conglomerate lenses and are overlain unconformably by folded Pliocene-Pleistocene Saugus Formation fanglomerate. The San Gabriel Fault Zone cuts both units. Marine macrofossils from the Gold Canyon beds give an age of 5.2+-0.3 Ma by 87Sr/86Sr analyses. Magnetic polarity stratigraphy dates deposition of the overlying Saugus Formation to between 2.6 Ma and 0.78 Ma. Distinctive metaplutonic rocks of the Mount Lowe intrusive suite in the San Gabriel Range are the source of certain clasts in both the Gold Canyon beds and Saugus Formation. Angular clasts of nondurable Paleocene sandstone also occur in the Gold Canyon beds. The large size and angularity of some of the largest of both clast types in breccia-conglomerate lenses of the beds suggest landslides or debris flows from steep terrain. Sources of Mount Lowe clasts, originally to the north or northeast, are now displaced southeastward by faulting and are located between the San Gabriel and Vasquez Creek faults, indicating as much as 12+-2 km of post-Miocene Vasquez Creek Fault right separation, in accord with some prior estimates. Post-Miocene right slip thus transferred onto the Vasquez Creek Fault southeast of the bifurcation. The right separation on the Vasquez Creek Fault adds to the generally accepted 22-23 km of middle-late Miocene right separation established for the San Gabriel Fault east of the bifurcation, resulting in total right separation of 34-35 km northwest of the bifurcation. Clast sizes and lithologies in Saugus Formation deformed alluvial fan deposits in the Gold and Little Tujunga Canyons area indicate that alluvial stream flow was from the north or north-northeast. The alluvial fan complex is beheaded at the San Gabriel Fault Zone, and no correlative deposits have been found north of the fault zone. Likely sources of several distinctive clast types are east of the bifurcation and north of the Vasquez Creek Fault. Combining these data with right slip caused by the 34 deg +-6 deg of clockwise local block rotation suggests that post-Saugus Formation (<2.6 to 0.78 Ma) right separation along the fault zone is 4+-2 km. The fossils, lithology, and age of the Gold Canyon beds correlate with the basal Pico Formation. The beds presumably connected southward or southwestward to a more open marine setting. A search for correlative strata to the south and southwest found that some strata previously mapped as Towsley Formation correlate with the Modelo Formation. Oyster spat in some Modelo Formation beds are the first recorded fossil occurrences and are especially remarkable because of associations with Miocene bathyal benthic foraminifers, planktonic calcareous nannofossils, and diatoms. Topanga Group basalt resting on basement rocks between Little and Big Tujunga Canyons gives an age of 16.14+-0.05 Ma from 40Ar/39Ar analysis. Improved understanding of the upper Miocene stratigraphy indicates large early movement on the eastern Santa Susana Fault at about 7-6 Ma.

Professional Paper↗
USGS2008

Comments on potential geologic and seismic hazards affecting proposed liquefied natural gas site in Santa Monica Bay, California

In a letter to the U.S. Geological Survey (USGS) dated March 25, 2008, Representative Jane Harman (California 36th district) requested advice on geologic hazards that should be considered in the review of a proposed liquefied natural gas (LNG) facility off the California coast in Santa Monica Bay. In 2004, the USGS responded to a similar request from Representative Lois Capps, regarding two proposed LNG facilities offshore Ventura County, Calif., with a report summarizing potential geologic and seismic hazards (Ross and others, 2004). The proposed LNG Deepwater Port (DWP) facility includes single point moorings (SPMs) and 35 miles of underwater pipelines. The DWP submersible buoys, manifolds, and risers would be situated on the floor of the southern Santa Monica Basin, in 3,000 feet of water, about 23 miles offshore of the Palos Verdes Peninsula. Twin 24-inch diameter pipelines would extend northeastward from the buoys across the basin floor, up the basin slope and across the continental shelf, skirting north around the Santa Monica submarine canyon. Figure 1 provides locations of the project and geologic features. Acronyms are defined in table 1. This facility is being proposed in a region of known geologic hazards that arise from both the potential for strong earthquakes and geologic processes related to sediment transport and accumulation in the offshore environment. The probability of a damaging earthquake (considered here as magnitude 6.5 or greater) in the next 30 years within about 30 miles (50 km) of the proposed pipeline ranges from 16% at the pipeline's offshore end to 48% where it nears land (Petersen, 2008). Earthquakes of this magnitude are capable of producing strong shaking, surface fault offsets, liquefaction phenomena, landslides, underwater turbidity currents and debris flow avalanches, and tsunamis. As part of the DWP license application for the Woodside Natural Gas proposal in Santa Monica Bay (known as the OceanWay Secure Energy Project), Fugro West, Inc., had already prepared a document discussing geologic hazards in the area, titled 'Exhibit B Topic Report 6 - Geological Resources' (Fugro West, Inc., 2007); hereafter, this will be called the 'Geological Resources document'. The USGS agreed to evaluate the information in the Geological Resources document regarding (1) proximity of active faults to the proposed project, (2) potential magnitude of seismic events from nearby faults, (3) thoroughness of the assessment of earthquake hazards in general, (4) potential hazards from ground rupture and strong shaking, (5) potential hazards from tsunamis, and (6) other geologic hazards including landslides and debris flows. Because two new earthquake probability reports were scheduled to be released in mid-April, 2008, by the USGS and the California Geological Survey (CGS), the USGS suggested a 6-month review period to enable a thorough incorporation of this new information. Twenty-seven scientists from the USGS and the CGS reviewed various sections of the Geological Resources document. This report outlines our major conclusions. The appendix is a longer list of comments by these reviewers, grouped by section of the Geological Resources document. Before discussing our reviews, we first provide a brief overview of geologic hazards in the proposed site area. This report is a snapshot in time and any future work in the area will need to take into account ongoing research efforts. For example, USGS scientists collected seismic reflection data in the spring of 2008 to study the structure and seismic potential of several faults in the area. Their interpretations (Conrad and others, 2008a and 2008b) are too preliminary to be included in this report, but their final results, along with other researchers' studies in the project area, should be considered in any future work on the Deepwater Port project.

California↗
USGS2004

Mid-Tertiary isopach and lithofacies maps for the Los Angeles region, California: Templates for palinspastic reconstruction to 17.4 Ma

A preliminary palinspastic reconstruction is presented of the region of the Los Angeles Basin at its 17.4 Ma inception. To create this reconstruction, pertinent paleomagnetic declination data are combined with new maps of the areal extent, thickness variations, and depositional facies of the >17.4 Ma Sespe-Vaqueros Formations and their equivalents. Opening of the Neogene Los Angeles Basin began abruptly about 17.4 Ma. Extensional rifting, with local basaltic volcanism, began the process and accompanied its early stages. Crustal detachment, followed by clockwise tectonic rotation and translation of large crustal blocks has been shown by previous paleomagnetic declination measurements in the western Transverse Ranges Province northwest of the basin and by large strike-slip and dip-slip separations on several major faults transecting it. Successful palinspastic reconstruction of the region to its arrangement before 17.4 Ma depends on understanding and integration of many stratigraphic and structural components. Before 17.4 Ma, fluviatile, alluvial and floodplain deposits, interstratified in the younger part with shallow marine to deeper shelf transgressive equivalents, accumulated to thicknesses as great as several kilometers. This report maps the surface and subsurface extents, thickness variations, and facies patterns of these strata, the Sespe plus Vaqueros and Trancas Formations or equivalents. Separate southeast and northwest sectors are revealed, each with distinctive internal thickness and facies patterns, which must have been related before rifting and transrotation. Terrestrial vertebrate and marine molluscan and foraminiferal fossils, plus magnetostratigraphic profiles of other workers and a few dates of igneous rocks, provide timing for key depositional and structural events. Our preliminary reconstruction of the region brings the internal patterns of the northwest and southeast sectors toward congruity but leaves unsatisfied discrepancies that suggest important information is missing. The reconstruction focuses attention on critical elements, specific uncertainties, and defi- ciencies of prior reconstructions. It also provides a new foundation for further work.

California↗
USGS2002

Age and tectonic significance of volcanic rocks in the northern Los Angeles Basin, California

Volcanic rocks, mostly basalts and some andesites, are interbedded with middle Miocene strata and are overlain by younger rocks throughout the greater part of the Los Angeles Basin, California. Roughly correlative flows, previously dated radiometrically (or paleontologically) at about 16.4 to 10.7 Ma, crop out in five separate regions around the basin perimeter. Los Angeles Basin volcanic rocks have special meaning because they offer clues to tectonomagmatic events associated with onset of clockwise transrotation of the western Transverse Ranges region and to the timing and locus of the initial basin opening. Whole-rock 40 Ar/ 39 Ar dating of near-tholeiitic olivine basalts of the Topanga Formation (Hoots, 1931) from three sites in the easternmost Santa Monica Mountains, combined with 87 Sr/ 86 Sr dating of fossil carbonates from interstratified marine beds at nine sites, establish a new age of 17.4 Ma for these oldest known Topanga-age volcanics of the Los Angeles Basin. We also record three new 40 Ar/ 39 Ar ages (15.3 Ma) from andesitic flows of the lower Glendora Volcanics at the northeast edge of the basin, 70 km east of the Santa Monica Mountains. A whole-rock determination of 17.2±0.5 Ma for nearby altered olivine basalt in the unfossiliferous Glendora volcanic sequence is questionable because of a complex 40 Ar/ 39 Ar age spectrum suggestive of 39Ar recoil, but it may indicate an older volcanic unit in this eastern area. We hypothesize that the 17.4-Ma volcanics in the eastern Santa Monica Mountains are an early expression of deep crustal magmatism accompanying the earliest extensional tectonism associated with rifting. The extremely thick younger volcanic pile in the western and central parts of the range may suggest that this early igneous activity in the eastern area was premonitory. Paleomagnetic declination data are needed to determine the pre-transrotational orientation of the eastern Santa Monica Mountains volcanic sequence. The new age determinations do not yield unequivocal support for either of two proposed explanations of possible age trends of Miocene volcanic rocks in southern California but underscore the need for further work.

California↗
USGS2001

Mountain Meadows Dacite: Oligocene intrusive complex that welds together the Los Angeles Basin, northwestern Peninsular Ranges, and central Transverse Ranges, California

Dikes and irregular intrusive bodies of distinctive Oligocene biotite dacite and serially related hornblende latite and felsite occur widely in the central and eastern San Gabriel Mountains, southern California, and are related to the Telegraph Peak granodiorite pluton. Identical dacite is locally present beneath Middle Miocene Topanga Group Glendora Volcanics at the northeastern edge of the Los Angeles Basin, where it is termed Mountain Meadows Dacite. This study mapped the western and southwestern limits of the dacite distribution to understand the provenance of derived redeposited clasts, to perceive Neogene offsets on several large strike-slip faults, to test published palinspastic reconstructions, and to better understand the tectonic boundaries that separate contrasting pre-Tertiary rock terranes where the Peninsular Ranges meet the central and western Transverse Ranges and the Los Angeles Basin. Transported and redeposited clasts of dacite-latite occur in deformed lower Miocene and lower middle Miocene sandy conglomerates (nonmarine, nearshore, and infrequent upper bathyal) close to the northern and northeastern margins of the Los Angeles Basin for a distance of nearly 60 km. Tie-lines between distinctive source suites and clast occurrences indicate that large tracts of the ancestral San Gabriel Mountains were elevated along range-bounding faults as early as 16–15 Ma. The tie-lines prohibit very large strike-slip offsets on those faults. Transport of eroded dacite began south of the range as early as 18 Ma. Published and unpublished data about rocks adjacent to the active Santa Monica-Hollywood-Raymond oblique reverse left-lateral fault indicate that cumulative left slip totals 13–14 km and total offset postdates 7 Ma. This cumulative slip, with assembly of stratigraphic and paleogeographic data, invalidates prior estimates of 60 to 90 km of left slip on these faults beginning about 17–16 Ma. A new and different palinspastic reconstruction of a region southwest of the San Andreas Fault Zone is proposed. Our reconstruction incorporates 20° of clockwise rotation of tracts north of the Raymond Fault from the easternmost Santa Monica Mountains to the Vasquez Creek Fault (San Gabriel south branch). We interpret the Vasquez Creek Fault as a reverse and right-lateral tear fault. Right slip on the tear becomes reverse dip slip on the northeast-striking Clamshell-Sawpit fault complex, interpreted as an offset part of the Mount Lukens Fault. This explains the absence of evidence for lateral offset of the Glendora Volcanics and associated younger marine strata where those are broken farther east by the eastern Sierra Madre reverse fault system. About 34 km of right slip is suggested for all breaks of the San Gabriel fault system. New paleogeographic maps of the Paleogene basin margin and of a Middle Miocene marine embayment and strandline derive in part from our palinspastic reconstruction. These appealingly simple maps fit well with data from the central Los Angeles Basin to the south and southwest.

California↗
USGS1979

Terrain corrections for borehole gravity measurements

This note presents examples of terrain corrections calculated for borehole gravity surveys made in a variety of topographic settings. The effect of terrain corrections on vertical density profiles calculated from borehole gravity measurements also is shown.

Geophysics↗
USGS1979

Terrain corrections for borehole and tower gravity measurements

Many investigators have computed terrain corrections for gravity measurements made in vertical mine shafts (e.g., Rogers, 1952; Domzalski, 1954; Rische, 1957; Vaschilov, 1964) and on structures above ground (e.g., Hammer, 1938; Kumagai et al., 1960; Kuo et al., 1969; Fajklewicz, 1976). The need for a rapid method for calculating terrain corrections for borehole gravity surveys arose with the development of a high-precision borehole gravity meter (Howell et al., 1966; McCulloh et al., 1967). Hearst (1968) was the first to publish a reasonable scheme for rapid computation of terrain corrections to both tower and borehole gravity surveys. Beyer (1971) applied terrain corrections to both tower and borehole gravity measurements using a computational procedure that increased the versatility of Hearst's method. Specific procedures are given by Beyer and Corbato (1972).

Open-File Report↗
USGS1971

The vertical gradient of gravity in vertical and near vertical boreholes

The vertical gradient of gravity is the rate of change of gravity in the direction of the plumb line. For a vertical borehole interval, it is approximated by the ratio of the gravity difference to the height difference as measured between the end points of the interval. The borehole vertical gradient is strongly affected by the densities of the rocks laterally adjacent to the well. Because of this useful effect, vertical (gravimetric) density profiles of the rooks adjacent to the borehole can be calculated from the borehole vertical gradients. A second useful effect, termed the "anomalous" vertical gradient, is caused by non-level equal-density surfaces related to the local and regional geology. The anomalous vertical gradient can enhance exploration beyond the confines of the borehole although it is a small and commonly negligible effect. These two useful effects are not determinable with absolute accuracy from observed borehole vertical gradients without independent subsurface rock density and (or) surface gravity information. In this study observed vertical gradients from high-precision, detailed gravity surveys made in seven shallow oil wells that penetrate a late Cenozoic sequence of marine and non-marine rocks in the Midway-Sunset Oil Field, California, are interpreted to obtain vertical density profiles. These gravimetric density profiles are adjusted 1) for anomalous vertical gradients calculated from surface gravity maps end, alternatively, measured on a portable tower and 2) for small extraneous effects of surface topography. The unadjusted and adjusted density profiles are compared with density measurements of core samples. The unadjusted density profiles of six wells are on the average systematically greater than core densities by .05 g/cm 3 . Adjusted profiles for the same wells agree with core densities to within .01 g/cm 3 on the average. Densities of an adjusted profile of a seventh well are .15 g/cm 3 less than those of the unadjusted profile and are in better agreement with core densities by that amount. However, residual systematic discrepancies between core and gravimetric densities for this seventh well indicate a measurable variation of the anomalous vertical gradient with depth and (or) lack of representative core density data. Topographic effects and anomalous vertical gradients in boreholes are usually small and change slowly with depth but, in some instances, may be comparatively large and change rapidly with depth. In the former case, gravimetric density profiles unadjusted for these effects can be in error by as much as about .05 g/cm 3 and, in the latter case, by as much as several tenths of a g/cm 3 . In both cases, relative errors between neighboring parts of the density profiles are much smaller. In cases where the anomalous vertical gradient changes appreciably with depth, it cannot be reliably estimated in the borehole from surface gravity measurements or from tower gradient measurements, which are especially sensitive to very shallow local density irregularities. At any borehole depth the anomalous gradient can be estimated from the difference between core and gravimetric densities of the same borehole interval. The core densities must be highly accurate and representative of the interval and the gravimetric density must he adjusted for topographic effects. Measured borehole vertical gradients have precisions of .00025 to .00050 mgal/ft (8 to 16 Eotvos units) for vertical intervals as small as 10 feet (3 meters); this meets the most stringent requirements of recognized applications for borehole gravimetry. An ideal borehole density logging device would be an in-motion continuously recording vertical gravity gradiometer.

Open-File Report↗