USGS Science⌕ Search

Geology topics

Michael J. Rymer

Publications and source records attributed to Michael J. Rymer.

At least 37 records · Page 2Linked to original sources
USGS2006

Map showing features and displacements of the Scenic Drive landslide, La Honda, California, during the period March 31, 2005–November 5, 2006

The Scenic Drive landslide in La Honda, San Mateo County, California began movement during the El Ni ñ o winter of 1997-98. Recurrent motion occurred during the mild El Ni ñ o winter of 2004-2005 and again during the winter of 2005-06. This report documents the changing geometry and motion of the Scenic Drive landslide in 2005-2006, and it documents changes and persistent features that we interpret to reflect underlying structural control of the landslide. We have also compared the displacement history to near-real time rainfall history at a continuously recording gauge for the period October 2004-November 2006.

California↗
USGS2005

Preliminary report on the 28 September 2004, M 6.0 Parkfield, California earthquake

The M w 6.0 Parkfield earthquake struck central California at 17:15:14 UTC on 28 September 2004. The epicenter was located 11 km southeast of the rural town of Parkfield, adjacent to Gold Hill and on the San Andreas Fault ( Figure 1 ). The California Integrated Seismic Network (CISN) reported that the hypocenter was located at 35.819°N, 120.364°W at a depth of 8.8 km. From the distribution of aftershocks and from models of seismograms, strain changes, and geodetic displacements from the earthquake, it appears that the rupture propagated to the northwest along the San Andreas Fault from its hypocenter beneath Gold Hill to Middle Mountain. Because of the earthquake's moderate size and the low population density, only minimal damage was reported, but strong ground motions of approximately 1 g were recorded at a few isolated points (Shakal et al. , 2005, this issue).

California↗
USGS2004

Photomosaics and logs of trenches on the San Andreas Fault, Thousand Palms Oasis, California

We present photomosaics and logs of the walls of trenches excavated for a paleoseismic study at Thousand Palms Oasis (Fig. 1). The site is located on the Mission Creek strand of the San Andreas fault zone, one of two major active strands of the fault in the Indio Hills along the northeast margin of the Coachella Valley (Fig. 2). The Coachella Valley section is the most poorly understood major part of the San Andreas fault with regard to slip rate and timing of past large-magnitude earthquakes, and therefore earthquake hazard. No large earthquakes have occurred for more than three centuries, the longest elapsed time for any part of the southern San Andreas fault. In spite of this, the Working Group on California Earthquake Probabilities (1995) assigned the lowest 30-year conditional probability on the southern San Andreas fault to the Coachella Valley. Models of the behavior of this part of the fault, however, have been based on very limited geologic data. The Thousand Palms Oasis is an attractive location for paleoseismic study primarily because of the well-bedded late Holocene sedimentary deposits with abundant layers of organic matter for radiocarbon dating necessary to constrain the timing of large prehistoric earthquakes. Previous attempts to develop a chronology of paleoearthquakes for the region have been hindered by the scarcity of in-situ 14C-dateable material for age control in this desert environment. Also, the fault in the vicinity of Thousand Palms Oasis consists of a single trace that is well expressed, both geomorphically and as a vegetation lineament (Figs. 2, 3). Results of our investigations are discussed in Fumal et al. (2002) and indicate that four and probably five surface-rupturing earthquakes occurred along this part of the fault during the past 1200 years. The average recurrence time for these earthquakes is 215 ± 25 years, although interevent times may have been as short as a few decades or as long as 400 years. Thus, although the elapsed time since the most recent earthquake, about 320 years, is about 50% longer than the average recurrence time, it is not necessarily unprecedented.

California↗
USGS2001

Surface Fractures Formed in the Potrero Canyon, Tapo Canyon, and McBean Parkway Areas in Association with the 1994 Northridge, California Earthquake

INTRODUCTION The magnitude 6.7 (M6.7) Northridge earthquake of 17 January 1994 strongly shook the Los Angeles urban region, resulting in 33 direct deaths, more than 20,000 people forced out of their homes, and an estimated $20 billion in damage (Hall, 1994). The earthquake was caused by slip on a previously unrecognized south-dipping fault buried beneath the San Fernando Valley. Slip on the fault propagated from a depth of about 19 km to about 8 km below the ground surface (USGS and SCEC, 1994). Although there was no surface faulting associated with the causative fault, surface fractures did develop along at least one fault (Mission Wells fault) and also in areas without recognized faults (Hart and others, 1995; Hecker and others, 1995a, 1995b; Rymer and others, 1995; Treiman, 1995). The term 'surface fractures' is used herein to describe ground breakage that is not associated with primary faulting or with triggered, secondary, surface faulting on a deep seismogenic fault. This report describes fault- and nonfault-related surface fractures that occurred at three sites, Potrero Canyon, Tapo Canyon, and the McBean Parkway area, 22 to 28 km north-northwest of the main shock (Fig. 1). Investigation of these sites documents far reaching effects of even moderately large earthquakes. Study of such effects has become increasingly important with further urbanization and development. Hecker and others (1995a, 1995b) documented the distribution of surface deformation associated with the Northridge earthquake in the Granada Hills area. The search for surface faulting and surface fracturing was initiated within hours of the earthquake. Both ground and airborne searches were made of the region. After fresh surface fractures were found in Potrero Canyon, aerial photographs were taken of the area (including the McBean Parkway site) by I.K. Curtis, on 21 January 1994, at scales of about 1:2,000 and 1:6,000. These aerial photographs were studied under high magnification to supplement ground-based observations of surface fractures.

Miscellaneous Field Studies Map↗
USGS2000

Hydrogeology of the regional aquifer near Flagstaff, Arizona, 1994-97

Sandstones, siltstones, and limestones that are Pennsylvanian to Permian in age underlie the southern part of the Colorado Plateau near Flagstaff, Arizona, and contain a complex regional aquifer that has become increasingly important as a source of water for domestic, municipal, and recreational uses. Ground-water flow in the regional aquifer is poorly understood in this area because (1) depth of the aquifer limits exploratory drilling and testing and (2) the geologic structure increases the complexity of the aquifer characteristics and the ground-water flow system. Four methods were used to improve the understanding of the hydrogeology of the regional aquifer near Flagstaff. • Remote-sensing techniques and geologic mapping provided data to identify many structural features that indicate a more complex structural environment and history than previously realized. • Data from surface-geophysical techniques that included ground-penetrating radar, seismic reflection and seismic refraction, and square-array resistivity, verified that some of the geologic structures expressed at land surface propagate deep into the subsurface and through the principal water-bearing zones of the regional aquifer at near-vertical angles. • A well and spring inventory, borehole-geophysical methods, and well and aquifer tests provided additional information relating aquifer and ground-water flow characteristics to geologic structure. • Water-chemistry data, which included major ion, nutrient, trace-element, and radioactive and stable-isotope analyses, provided an independent means of verifying the hydrogeologic characteristics of the aquifer and were used to determine recharge and discharge areas, groundwater movement, and ground-water age. Ground-water recharge occurs throughout the area but is greatest at higher altitudes where precipitation is greater and in areas where heavily fractured rock units of the aquifer are exposed. The estimated annual average recharge to the regional aquifer in the study area is about 290,000 acre-feet. Ground water flows laterally and vertically through pore spaces in the rock and along faults and other fractures from high-altitude areas in the southern part of the study area to regional drains north of the study area along the Little Colorado and Colorado Rivers, and to drains south of the study area along Oak Creek and the Verde Valley. Ground-water discharge in these areas—about 400,000 acre-feet per year—exceeds the annual recharge to the aquifer in the Flagstaff area, but ground water from areas outside the study area contributes to this discharge as well. The saturated thickness of the regional aquifer averages about 1,200 feet, and the amount of water in storage could be as much as 4,800,000 acrefeet, or about 10 percent of the total volume of the aquifer. The quality of water in the regional aquifer in terms of dissolved-solids concentrations is good for most uses throughout the area. Dissolvedsolids concentrations generally are less than 500 milligrams per liter. Water in the regional aquifer is primarily a calcium magnesium bicarbonate type. In some areas near the Rio de Flag, the water has significant nitrate and chloride components, which indicate direct recharge in these areas from the Rio de Flag. Oxygen and deuterium data indicate a common recharge source for water in the aquifer and that some sites receive recharge from surface waters where evaporation has occurred. Estimated carbon-14 ages and tritium activities indicate ground-water ages from less than 200 years in the Lake Mary area to more than 5,000 years in the Wupatki area. The regional aquifer is heterogeneous and anisotrophic and has a complex ground-water flow system. The most productive water-bearing material tends to be fine- to medium-grained sandstones, and ground-water flow and potential well yields are related to geologic structure. Fracturing associated with structural deformation increases recharge locally and also increases the potential for high well yields. Surface-geophysical techniques provided information on the orientation of high-angle, deep-seated structure in the saturated zone. Borehole-geophysical data identified horizontal to near-horizontal fractures as significant components of the fracture-flow system not apparent in the surface-geophysical data. Structural features that strike northwest appear to be areas that have the greatest potential for high well yields. A north-northeastward-striking structure may be just as promising, but additional data are needed to verify this relation.

Arizona↗
USGS1998

Scenic drive landslide of January-March 1998, La Honda, San Mateo County, California

The small rural town of La Honda, Calif., is an unincorporated region of San Mateo County situated in the Santa Cruz Mountains in the western part of the San Francisco peninsula. Much of the town is underlain by a previously recognized ancient landslide complex. The ancient slide complex covers about 1.0 to 1.25 km2, parts of which have been historically active. This report describes a recent landslide involving part of Scenic Drive, La Honda, that became active in January 1998. This report does not describe other currently active landslides in La Honda, such as the January 1998 slide on lower Recreation Drive, or the history of sliding in the area. This report concerns the principal morphological features we observed and mapped between 11 February and 21 March 1998 on an enlargement of a 1:7500-scale air photo acquired 6 March 1998 and prior to that on a town property-line map, and by laser survey carried out between 26 February and 8 March. The principal objective of this report is to make available the detailed photographic and topographic base maps and associated description of surface morphological features.

Open-File Report↗
USGS1992

The 1992 Landers earthquake and surface faulting

Faulting associated with the June 28, 992, earthquake near Landers, California, broke the surface of the ground over a length of more than 70 km, the longest surface rupture in the United States since the great San Francisco quake of 1906. the strongest shaking associated with this magnitude 7.6 (M S ) earthquake, the largest in the contiguous 48 states in the last 40 years, occurred in a sparsely populated sections of the Mojave Desert more than 200 km east of Los Angeles. the earthquake began with a sudden slip on the Johnson Valley fault about 10 km southwest of Landers. The initial fault movement probably occurred at a depth of less than 10 km. Surface faulting then propagated over 70 km to the north and northeast. The faulting linked preexisting faults-some previously known and mapped and others previously unknown-into a complex, coherent rupture zone.

California↗
USGS1988

Depositional environments of the Cache, Lower Lake, and Kelseyville Formations, Lake County, California

We describe the depositional environments of the Cache, Lower Lake, and Kelseyville Formations in light of habitat preferences of recovered mollusks, ostracodes, and diatoms. Our reconstruction of paleoenvironments for these late Cenozoic deposits provides a framework for an understanding of basin evolution and deposition in the Clear Lake region. The Pliocene and Pleistocene Cache Formation was deposited primarily in stream and debris flow environments; fossils from fine-grained deposits indicate shallow, fresh-water environments with locally abundant aquatic vegetation. The fine-grained sediments (mudstone and siltstone) were probably deposited in ponds in abandoned channels or shallow basins behind natural levees. The abandoned channels and shallow basins were associated with the fluvial systems responsible for deposition of the bulk of the technically controlled Cache Formation. The Pleistocene Lower Lake Formation was deposited in a water mass large enough to contain a variety of local environments and current regimes. The recovered fossils imply a lake with water depths of 1 to 5 m. However, there is strong support from habitat preferences of the recovered fossils for inferring a wide range of water depths during deposition of the Lower Lake Formation; they indicate a progressively shallowing system and the culmination of a desiccating lacustrine system. The Pleistocene Kelseyville Formation represents primarily lacustrine deposition with only minor fluvial deposits around the margins of the basin. Local conglomerate beds and fossil tree stumps in growth position within the basin indicate occasional widespread fluvial incursions and depositional hiatuses. The Kelseyville strata represent a large water mass with a muddy and especially fluid substrate having permanent or sporadic periods of anoxia. Central-lake anoxia, whether permanent or at irregular intervals, is the simplest way to account for the low numbers of benthic organisms recovered from the Kelseyville Formation. Similar low-oxygen conditions for benthic life are represented throughout the sedimentary history of Clear Lake. Water depths for the Kelseyville Formation of 10 to 30 m and 12 m near the margins of the basin are inferred both before and after fluvial incursions. These water-depth fluctuations cannot be correlated with major climatic changes as indicated by pollen and fossil leaves and cones; they may be due to faulting in this technically active region.

GSA Special Papers↗
USGS1981

Sample catalog for core CL-80-1, Clear Lake, Lake County, California

A 177-m-long core designated CL-80-1 was taken from Clear Lake, Calif., during July and August, 1980, at latitude 39.08°N, longitude 122.84°W (fig. 1). The core was removed from Clear Lake for interdisciplinary studies and regional correlation of paleoclimates, paleoecologies, paleolimnology, Quaternary dating techniques, and frequency of volcanic eruptions. This catalog is designed to help investigators identify samples taken from the core that are most appropriate for their discipline.

California↗
USGS1981

Description and preliminary interpretation of core CL-80-1, Clear Lake, Lake County, California

Coring operations were conducted in the west basin of Clear Lake during July and August 1980 to produce a regional Quaternary reference section. A 177-m-long core (CL-80-1) was taken, which also augments and extends a previous study of eight shorter cores collected from Clear Lake in 1973. Core CL-80-1 was continuously cored in 7.5 m of water, and 66.5 percent recovery was achieved. The sediments are composed primarily of clayey and silty sapropelic mud similar to those presently being deposited in the lake, and are interbedded with local coarse sand and gravel deposits and thin volcanic ash beds. Coring was terminated when coarse rounded gravel and cobbles of Franciscan assemblage lithology were encountered. The location of core CL-80-1 is between two other core sites of the 1973 series of cores, one of which (CL-73-4) is 115 m long and contains a well-defined, uninterrupted pollen and physical stratigraphic record from the present to about 130,000 years ago. Paleomagnetic and preliminary pollen analyses of core CL-80-1 are complete and comparison of these results with those of core CL-73-4 suggest that the new core represents a record from the present to about 175,000 years ago.

California↗
USGS1978

Stratigraphy of the Cache Formation (Pliocene and Pleistocene) in Clear Lake Basin, Lake County, California

Recent geologic mapping in the Clear Lake basin shows that the nonmarine Cache Formation can be subdivided into several members. New names are herein informally used for three distinct deposits called the B, L, and K members. The three members are geographically separate, except where the L member locally unconformably overlies the B member. This study of the Cache Formation provides a framework for understanding the late Cenozoic tectonic, geologic, and climatic histories of the Clear Lake, California, area. The B member is characterized by cross-stratified sandstone with interbedded reddish-brown conglomerate around the margins of the basin, and by gray sandstone and persistent, light-olive-gray conglomerate lower in the section, as it is exposed in the center of the basin. Minor amounts of basaltic tuff are present near the top of the B member in the Clear Lake basin. The B member has a maximum thickness of at least 1,500 m and represents dominantly fluvial and minor lacustrine deposition. This Blancan (Pliocene and early Pleistocene(?)) unit was deposited in a fault-controlled, subsiding basin. The L member is a heterogeneous deposit of pebble conglomerate, sandstone, siltstone, calcareous siltstone, limestone, tuff, and diatomite. This lacustrine unit has a maximum thickness of at least 130 m, and is mid-Pleistocene in age. The K member is composed of lacustrine sandstone and siltstone, and locally interbedded fluvial pebble conglomerate and sandstone. Several tuffs, including the tuff of Adobe Creek, an informally named marker bed, occur in the K member. The K member has a maximum thickness of at least 140 m and is mid-Pleistocene in age. The presence of fossil leaves and cones that represent growth during warm and cold climates indicate that the K member was deposited during both interglacial and glacial climatic conditions. The tuff of Adobe Creek of the K member has been recognized in water wells west and north of surface exposures of the K member. The B member is probably correlative with the Tehama Formation and is apparently unrelated to the sediment of Clear Lake. The L and K members intertongue with and are underlain by flows of the Clear Lake Volcanics. The L and K members are dominated by partly coeval lacustrine deposits that were possibly deposited in different subbasins of the same lake, and are possibly correlative with sediment concealed beneath Clear Lake.

California↗
USGS1976

Preliminary description and interpretation of cores and radiographs from Clear Lake, Lake County, California: Core 3

Clear Lake, California is located in the California Coast Ranges about 120 km north of San Francisco and is the largest freshwater lake wholly within California. The lake basin is tectonically controlled (Anderson, 1936; Brice, 1953; Sims and Rymer, 1974) and the area seismically active (Coffman and von Hake, 1973). Interest in this lake was stimulated by hypotheses developed from a study of sediments in Van Norman Reservoir after the 1971 San Fernando earthquake (Sims, 1973). During this study three zones of deformational structures were found in the 1 m-thick sequence of sediments exposed over about 2 km2 of the reservoir bottom. These zones were correlated with moderate earthquakes that shook the San Fernando area in 1930, 1952, and 1971. Results of this study, coupled with the experimental formation of deformational structures similar to those from Van Norman Reservoir, led to a search for similar structures in Pleistocene and Holocene lakes and lake sediments in other seismically active areas. Clear Lake, California was chosen specifically because of its location near the San Andreas fault and the San Francisco-Oakland urban complex, and the probability of obtaining an uninterrupted sediment record from the present into Pleistocene time. Eight 12 to 15 cm diameter continuous cores were taken from the lake sediments (fig. 1) as part of a study of earthquake induced structures in sediments and the tectonic framework of the Clear Lake basin. The eight cores range in length from 13.87 m to 115.21 m (Table 1).

California↗
USGS1976

Preliminary survey of modern glaciolacustrine sediments for earthquake-induced deformational structures, south-central Alaska

Bottom sediments of four lakes in South-Central Alaska were studied in the summer of 1975 for evidence of earthquake-induced deformation. The lakes are: Summit, Upper Trail, and Skilak, all on the Kenai Peninsula, and Eklutna, northeast of Anchorage (fig. 1). Interest in these lakes was stimulated by hypotheses developed from a study of sediments in Van Norman Reservoir, California, after the 1971 San Fernando earthquake (Sims, 1973). During that study three zones of deformational structures were found and correlated with moderate earthquakes that shook the San Fernando area in 1930, 1952, and 1971. Results of that study, coupled with the experimental formation of deformational structures similar to those from Van Norman Reservoir, led to a search for similar structures in Pleistocene and Holocene lakes and lake sediments in other seismically active areas. The lakes for this study were chosen specifically because of their location within the area affected by the 1964 Prince William Sound earthquake, and the probability of obtaining varved sediments which would allow counting of years between sedimentologic events.

Alaska↗