Geology topics
M. J. Rymer
Publications and source records attributed to M. J. Rymer.
High-resolution seismic reflection/refraction imaging from Interstate 10 to Cherry Valley Boulevard, Cherry Valley, Riverside County, California: Implications for water resources and earthquake hazards
This report is the second of two reports on seismic imaging investigations conducted by the U.S. Geological Survey (USGS) during the summers of 1997 and 1998 in the Cherry Valley area in California (Figure 1a). In the first report (Catchings et al., 1999), data and interpretations were presented for four seismic imaging profiles (CV-1, CV-2, CV-3, and CV-4) acquired during the summer of 1997 . In this report, we present data and interpretations for three additional profiles (CV-5, CV-6, and CV-7) acquired during the summer of 1998 and the combined seismic images for all seven profiles. This report addresses both groundwater resources and earthquake hazards in the San Gorgonio Pass area because the shallow (upper few hundred meters) subsurface stratigraphy and structure affect both issues. The cities of Cherry Valley and Beaumont are located approximately 130 km (~80 miles) east of Los Angeles, California along the southern alluvial fan of the San Bernardino Mountains (see Figure 1b). These cities are two of several small cities that are located within San Gorgonio Pass, a lower-lying area between the San Bernardino and the San Jacinto Mountains. Cherry Valley and Beaumont are desert cities with summer daytime temperatures often well above 100 o F. High water usage in the arid climate taxes the available groundwater supply in the region, increasing the need for efficient management of the groundwater resources. The USGS and the San Gorgonio Water District (SGWD) work cooperatively to evaluate the quantity and quality of groundwater supply in the San Gorgonio Pass region. To better manage the water supplies within the District during wet and dry periods, the SGWD sought to develop a groundwater recharge program, whereby, excess water would be stored in underground aquifers during wet periods (principally winter months) and retrieved during dry periods (principally summer months). The SGWD preferred a surface recharge approach because it could be less expensive than a recharging program based on injection wells. However, at an existing surface recharge site, surface recharge of the aquifer was limited by the presence of clayrich layers that impede the downward percolation of the surface water. In boreholes, these clay-rich layers were found to extend from the near surface to about 50 m depth. If practical, the SGWD desired to relocate the recharge ponds to another location within the Cherry Valley–Beaumont area. This required that sites be found where the clay-rich layers were absent. The SGWD elected to explore for such sites by employing a combination of drilling and seismic techniques. A number of near-surface faults have been suggested in the Cherry Valley-Beaumont area (Figure 1b). However, there may be additional unmapped faults that underlie the alluvial valley of San Gorgonio Pass. Because faults are known to act as barriers to lateral groundwater flow in alluvial groundwater systems, mapped and unmapped subsurface faults in the Cherry Valley-Beaumont area would likely influence groundwater flow and the lateral distribution of recharged water. These same faults may pose a significant hazard to the local desert communities and to greater areas of southern California due to the presence of lifelines (water, electrical, gas, transportation, etc.) that extend through San Gorgonio Pass to larger urban areas. The three principal goals of the seismic investigation presented in this report were to laterally map the subsurface stratigraphic horizons, locate faults that may act as barriers to groundwater flow, and measure velocities of shallow sediments that may give rise to amplified shaking during major earthquakes.
Faulting apparently related to the 1994 Northridge, California, earthquake and possible co-seismic origin of surface cracks in Potrero Canyon, Los Angeles County, California
Apparent southward-dipping, reverse-fault zones are imaged to depths of about 1.5 km beneath Potrero Canyon, Los Angeles County, California. Based on their orientation and projection to the surface, we suggest that the imaged fault zones are extensions of the Oak Ridge fault. Geologic mapping by others and correlations with seismicity studies suggest that the Oak Ridge fault is the causative fault of the 17 January 1994 Northridge earthquake (Northridge fault). Our seismically imaged faults may be among several faults that collectively comprise the Northridge thrust fault system. Unusually strong shaking in Potrero Canyon during the Northridge earthquake may have resulted from focusing of seismic energy or co-seismic movement along existing, related shallow-depth faults. The strong shaking produced ground-surface cracks and sand blows distributed along the length of the canyon. Seismic reflection and refraction images show that shallow-depth faults may underlie some of the observed surface cracks. The relationship between observed surface cracks and imaged faults indicates that some of the surface cracks may have developed from nontectonic alluvial movement, but others may be fault related. Immediately beneath the surface cracks, P-wave velocities are unusually low (<400 m/sec), and there are velocity anomalies consistent with a seismic reflection image of shallow faulting to depths of at least 100 m. On the basis of velocity data, we suggest that unconsolidated soils (<800 m/sec) extend to depths of about 15 to 20 m beneath our datum (<25 m below ground surface). The underlying rocks range in velocity from about 1000 to 5000 m/sec in the upper 100 m. This study illustrates the utility of high-resolution seismic imaging in assessing local and regional seismic hazards.
Seismic reflection and refraction investigations in Potrero Canyon, Los Angeles County, California
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Ground deformation in Granada Hills and Mission Hills resulting from the January 17, 1994, Northridge, California, earthquake
No abstract available.
Proceedings of Workshop XXVII; Mechanics of the May 2, 1983 Coalinga earthquake
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Preliminary slip-rate table and map of late-Quaternary faults of California
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Surface displacement on the Imperial and Superstition Hills faults triggered by the Westmorland, California, earthquake of 26 April 1981
Parts of the Imperial and the Superstition Hills faults moved right-laterally at the ground surface at the time of or shortly following the ML 5.6 Westmorland earthquake of 26 April 1981. The displacements occurred prior to any significant aftershocks on either fault and thus are classed as sympathetic. Although the main shock was located in an exceptionally seismogenic part of Imperial Valley, about 20 km distant from either fault, no clear evidence of surface faulting has yet been found in the epicentral area. Horizontal displacement on the Imperial and Superstition Hills faults, southeast and southwest of the epicenter, respectively, reached maxima of 8 mm and 14 mm, and the discontinuous surface ruptures formed along approximately equal lengths of northern segments of the two structures (16.8 km and 15.7 km, respectively). The maximum vertical component of slip on the Imperial fault, 6 ram, was observed 3.4 km north of the point of largest horizontal slip. Vertical movement on the Superstition Hills fault was less than 1 mm. No new displacement was found along the traces of the Brawley fault zone, the San Andreas fault, or the part of the Coyote Creek fault that slipped during the 1968 Borrego Mountain earthquake. A careful search in the epicentral area of the main shock failed to locate any definite evidence of surface faulting. Concentrations of late aftershocks north and northeast of Calipatria near the southeastward projection of the San Andreas fault occurred mostly after our field check; this area was not investigated.
Description and preliminary interpretation of core CL-80-2, Clear Lake, Lake County, California
Coring operations in the west basin of Clear Lake produced a regional Quaternary reference section to augment and extend a previous study of cores from Clear Lake. This report concerns 165.8—m—long core CL-80-2, which was continuously cored in 8.0 m of water and has a 65.0 percent recovery. The sedinents in core CL-80-2 are composed primarily of clayey and silty sapropelic mud that is similar to those presently being deposited in the lake. The core ended in coarse CO2—charged sand at 165.8 m. The age of sediment at the bottom of the core is inferred to be approximately 175,000 years.
Chemical composition of water and gas from five nearshore subaqueous springs in Clear Lake, Northern California
In 1971 The Geysers-Clear Lake area was selected by the U.S. Geological Survey geothermal research program as a region for extensive investigation. Under this program thermal water samples were first collected in December, 1974 during a winter of normal rainfall; the last samples were collected in February, 1977 during a period of drought. The drought exposed many springs which normally are submerged by Clear Lake. The collection and analysis of these springs is reported in Thompson and others (this vol.).
Map of gaseous springs and associated faults in Clear Lake, California
No abstract available.
Sampling procedures and catalogue of samples for eight boreholes at Clear Lake, Lake County, California
Clear Lake, California, is situated in an area which has been subject to crustal movement, earthquake-generated ground shaking, volcanic eruptions, and climatic fluctuations during late Quaternary time. The U.S. Geological Survey, in cooperation with Lake County, has undertaken a study of the seismic, volcanic, and environmental history recorded in the late Quaternary sediments beneath the floor of the lake (Sims, 1974). This study is based on continuous core samples measuring 12 cm or 15 cm in diameter that were obtained in August-November, 1973, from 8 boreholes measuring 14-113 m in length (Figure 1). Preliminary description of many of these samples and interpretation of ancient seismic events can be found in Sims and Rymer (1975). Over 2,000 multiple samples have been taken from these cores in order to study the environmental record preserved in the lacustrine sediments. Samples were taken for pollen, diatoms, cladocera, bulk mineralogy, fine size analysis, macrofossils, and water-content/organic carbon-content at designated depths. In addition, volcanic ash and radiocarbon samples were removed for correlation studies and age determinations. This report provides a description of the standard sampling procedures designed for sapropelic muds and peat-rich clays, a description of modified sampling procedures developed for sampling sands and coarser sediments, and a catalogue of samples from the Clear Lake cores. Table 2 outlines the steps followed for the standard sampling procedures.