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Results for “The Seismic Record”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 1,729 records · Page 96Linked to original sources
USGS1989

The role of catastrophic geomorphic events in central Appalachian landscape evolution

Catastrophic geomorphic events are taken as those that are large, sudden, and rare on human timescales. In the nonglaciated, low-seismicity central Appalachians, these are dominantly floods and landslides. Evaluation of the role of catastrophic events in landscape evolution includes assessment of their contributions to denudation and formation of prominent landscape features, and how they vary through space and time. Tropical storm paths and topographic barriers at the Blue Ridge and Allegheny Front create significant climatic variability across the Appalachians. For moderate floods, the influence of basin geology is apparent in modifying severity of flooding, but for the most extreme events, flood discharges relate mainly to rainfall characteristics such as intensity, duration, storm size, and location. Landslide susceptibility relates more directly to geologic controls that determine what intensity and duration of rainfall will trigger slope instability. Large floods and landslides are not necessarily effective in producing prominent geomorphic features. Large historic floods in the Piedmont have been minimally effective in producing prominent and persistent geomorphic features. In contrast, smaller floods in the Valley and Ridge produced erosional and depositional features that probably will require thousands of years to efface. Scars and deposits of debris slide-avalanches triggered on sandstone ridges recover slowly and persist much longer than scars and deposits of smaller landslides triggered on finer-grained regolith, even though the smaller landslides may have eroded greater aggregate volume. The surficial stratigraphic record can be used to extend the spatial and temporal limits of our knowledge of catastrophic events. Many prominent alluvial and colluvial landforms in the central Appalachians are composed of sediments that were deposited by processes similar to those observed in historic catastrophic events. Available stratigraphic evidence shows two scales of temporal variation: one related to Quaternary climate changes and a more-recent, higher-frequency variation due to rare events during the Holocene. In much of the central Appalachians, landforms related to Quaternary climate changes persist as the most prominent features, despite the modifying effects of late-Holocene catastrophic events.

Geomorphology↗
USGS2008

Exponential decline of aftershocks of the M7.9 1868 great Kau earthquake, Hawaii, through the 20th century

The remarkable catalog of Hawaiian earthquakes going back to the 1820s is based on missionary diaries, newspaper accounts, and instrumental records and spans the great M 7.9 Kau earthquake of April 1868 and its aftershock sequence. The earthquake record since 1868 defines a smooth curve complete to M 5.2 of the declining rate into the 21st century, after five short volcanic swarms are removed. A single aftershock curve fits the earthquake record, even with numerous M 6 and 7 main shocks and eruptions. The timing of some moderate earthquakes may be controlled by magmatic stresses, but their overall long‐term rate reflects one of aftershocks of the Kau earthquake. The 1868 earthquake is, therefore, the largest and most controlling stress event in the 19th and 20th centuries. We fit both the modified Omori (power law) and stretched exponential (SE) functions to the earthquakes. We found that the modified Omori law is a good fit to the M ≥ 5.2 earthquake rate for the first 10 years or so and the more rapidly declining SE function fits better thereafter, as supported by three statistical tests. The switch to exponential decay suggests that a possible change in aftershock physics may occur from rate and state fault friction, with no change in the stress rate, to viscoelastic stress relaxation. The 61‐year exponential decay constant is at the upper end of the range of geodetic relaxation times seen after other global earthquakes. Modeling deformation in Hawaii is beyond the scope of this paper, but a simple interpretation of the decay suggests an effective viscosity of 10 19 to 10 20 Pa s pertains in the volcanic spreading of Hawaii's flanks. The rapid decline in earthquake rate poses questions for seismic hazard estimates in an area that is cited as one of the most hazardous in the United States.

Hawaii↗
USGS2021

Which earthquake accounts matter?

Earthquake observations contributed by human observers provide an invaluable source of information to investigate both historical and modern earthquakes. Commonly, the observers whose eyewitness accounts are available to scientists are a self‐selected minority of those who experience a given earthquake. As such these may not be representative of the overall population that experienced shaking from the event. Eyewitness accounts can contribute to modern science only if they are recorded in the first place and archived in an accessible repository. In this study, we explore the extent to which geopolitics and socioeconomic disparities can limit the number of earthquake observers whose observations can contribute to science. We first revisit a late nineteenth‐century earthquake in the central United States in 1882 that provides an illustrative example of an event that has been poorly characterized due to a reliance on English‐language archival materials. For modern earthquakes, we analyze data collected for recent earthquakes in California and India via the online “Did You Feel It?” (DYFI) system. In California, online data‐collection systems appear to be effective in gathering eyewitness accounts from a broad range of socioeconomic groups. In India, however, responses to the DYFI system reveal a strong bias toward responses from urban areas as opposed to rural settlements, as well a bias with literacy rate. The dissimilarity of our results from modern earthquakes in the United States and India provides a caution that, in some parts of the world, contributed felt reports can still potentially provide an unrepresentative view of earthquake effects, especially if online data collection systems are not designed to be broadly accessible. This limitation can in turn potentially shape our understanding of an earthquake’s impact and the characterization of seismic hazard.

Arkansas, Oklahoma, Texas↗
USGS1972

Catalog of earthquakes along the San Andreas fault system in central California for the year 1971

A network of seismograph stations was established by the National Center for Earthquake Research (NCER) to study in detail the earthquakes along the San Andreas fault system in central California (Eaton, Lee, and Pakiser, 1970). This report, in the form of a catalog, summarizes the results of routine earthquake locations from that network for the year 1971, and provides the basic data for further studies to be published elsewhere. Similar catalogs for 1969 and 1970 have been prepared by Lee, Roller, Bauer, and Johnson, (1972), and Lee, Roller, Meagher, and Bennett, (1972). We located a total of 2,429 events that occurred in 1971 from primarily 34,111 first P-wave arrival times recorded at 121 seismograph stations. Among these events, 339 were blasts (mostly in quarries), 8 were suspected blasts, and 41 were either too far away from available stations or too small in magnitude to be adequately located. The remaining 2,041 events which were identified as earthquakes are presented in the catalog. The 121 seismograph stations consisted of 93 telemetered stations operated by NCER, and 28 stations operated by several other organizations. Readings from the latter stations were obtained through the courtesy of the Seismographic Stations, University of California, Berkeley, the Earthquake Mechanism Laboratory, National Oceanic and Atmospheric Administration, San Francisco, and the California Department of Water Resources, Sacramento. Data on local earthquakes in northern California, Nevada, and Oregon have been published in the Bulletins of the Seismographic Stations of the University of California, Berkeley (UCB) for many decades. The present catalog covers earthquakes which occurred in a smaller area but in greater detail than those covered by the UCB Bulletins. For example, the UCB Bulletins for 1971 (Cloud and Qamar, 1972; Cloud, Tomblin, and Litehiser, 1972) list a total of 116 earthquakes (most with magnitude greater than 2.5) in the region covered by this report (a coastal strip from Santa Rosa to Parkfield). In addition, we attempted to use all available data in locating earthquakes within and near our seismic network.

California↗
USGS2020

U.S. Geological Survey 2018 Kīlauea Volcano eruption response in Hawai'i—After-action review

The 2018 Kīlauea Volcano eruption lasted 107 days, and now ranks as the most destructive event at Kilauea since 1790, and as one of the most costly volcanic disasters in U.S. history. Multiple simultaneous hazard events unfolded, including sustained seismic activity leading to collapse at the summit of Halema'uma'u crater and severe damage to the HVO facility, with additional eruption of lava in the Kīlauea Lower East Rift Zone that progressively grew to a total of 24 fissure openings. In response to the complex and uncertain nature of the eruption, U.S. Geological Survey (USGS) team activities tended to coalesce around several interrelated core functional areas: science operations, emergency management and administration, and external communications. Upon cessation of the eruption, the USGS Hazard Response Executive Committee charged the Alaska Regional Office to lead an After-Action Review team, which focused on two basic questions: (1) what went well, and why?; and (2) what can be improved, and how? The purpose of the After-Action Review is to identify priorities for programmatic or policy improvements that the USGS can feasibly implement to advance strategic preparation for future disasters, and thereby reduce public vulnerabilities. Specifically, the review is intended to help USGS respond even better to the next eruption in Hawai'i or elsewhere by advancing any of the following goals: Design better planning scenarios; Enhance response team effectiveness; Assist local decision makers; Promote new areas of strategic research; and Streamline administrative, finance, and Incident Management Team support functions during a crisis to secure continuity of operations and essential records management.

Hawaii↗
USGS2017

Dynamic rupture modeling of the M7.2 2010 El Mayor-Cucapah earthquake: Comparison with a geodetic model

The 2010 M w 7.2 El Mayor-Cucapah earthquake is the largest event recorded in the broader Southern California-Baja California region in the last 18 years. Here we try to analyze primary features of this type of event by using dynamic rupture simulations based on a multifault interface and later compare our results with space geodetic models. Our results show that starting from homogeneous prestress conditions, slip heterogeneity can be achieved as a result of variable dip angle along strike and the modulation imposed by step over segments. We also considered effects from a topographic free surface and find that although this does not produce significant first-order effects for this earthquake, even a low topographic dome such as the Cucapah range can affect the rupture front pattern and fault slip rate. Finally, we inverted available interferometric synthetic aperture radar data, using the same geometry as the dynamic rupture model, and retrieved the space geodetic slip distribution that serves to constrain the dynamic rupture models. The one to one comparison of the final fault slip pattern generated with dynamic rupture models and the space geodetic inversion show good agreement. Our results lead us to the following conclusion: in a possible multifault rupture scenario, and if we have first-order geometry constraints, dynamic rupture models can be very efficient in predicting large-scale slip heterogeneities that are important for the correct assessment of seismic hazard and the magnitude of future events. Our work contributes to understanding the complex nature of multifault systems.

California↗
USGS2015

Update of the Graizer-Kalkan ground-motion prediction equations for shallow crustal continental earthquakes

A ground-motion prediction equation (GMPE) for computing medians and standard deviations of peak ground acceleration and 5-percent damped pseudo spectral acceleration response ordinates of maximum horizontal component of randomly oriented ground motions was developed by Graizer and Kalkan (2007, 2009) to be used for seismic hazard analyses and engineering applications. This GMPE was derived from the greatly expanded Next Generation of Attenuation (NGA)-West1 database. In this study, Graizer and Kalkan’s GMPE is revised to include (1) an anelastic attenuation term as a function of quality factor (Q0) in order to capture regional differences in large-distance attenuation and (2) a new frequency-dependent sedimentary-basin scaling term as a function of depth to the 1.5-km/s shear-wave velocity isosurface to improve ground-motion predictions for sites on deep sedimentary basins. The new model (GK15), developed to be simple, is applicable to the western United States and other regions with shallow continental crust in active tectonic environments and may be used for earthquakes with moment magnitudes 5.0–8.0, distances 0–250 km, average shear-wave velocities 200–1,300 m/s, and spectral periods 0.01–5 s. Directivity effects are not explicitly modeled but are included through the variability of the data. Our aleatory variability model captures inter-event variability, which decreases with magnitude and increases with distance. The mixed-effects residuals analysis shows that the GK15 reveals no trend with respect to the independent parameters. The GK15 is a significant improvement over Graizer and Kalkan (2007, 2009), and provides a demonstrable, reliable description of ground-motion amplitudes recorded from shallow crustal earthquakes in active tectonic regions over a wide range of magnitudes, distances, and site conditions.

Open-File Report↗
USGS2016

Late Holocene volcanism at Medicine Lake Volcano, northern California Cascades

Late Holocene volcanism at Medicine Lake volcano in the southern Cascades arc exhibited widespread and compositionally diverse magmatism ranging from basalt to rhyolite. Nine well-characterized eruptions have taken place at this very large rear-arc volcano since 5,200 years ago, an eruptive frequency greater than nearly all other Cascade volcanoes. The lavas are widely distributed, scattered over an area of ~300 km 2 across the >2,000-km 2 volcano. The eruptions are radiocarbon dated and the ages are also constrained by paleomagnetic data that provide strong evidence that the volcanic activity occurred in three distinct episodes at ~1 ka, ~3 ka, and ~5 ka. The ~1-ka final episode produced a variety of compositions including west- and north-flank mafic flows interspersed in time with fissure rhyolites erupted tangential to the volcano’s central caldera, including the youngest and most spectacular lava flow at the volcano, the ~950-yr-old compositionally zoned Glass Mountain flow. At ~3 ka, a north-flank basalt eruption was followed by an andesite eruption 27 km farther south that contains quenched basalt inclusions. The ~5-ka episode produced two caldera-focused dacitic eruptions. Quenched magmatic inclusions record evidence of intrusions that did not independently reach the surface. The inclusions are present in five andesitic, dacitic, and rhyolitic host lavas, and were erupted in each of the three episodes. Compositional and mineralogic evidence from mafic lavas and inclusions indicate that both tholeiitic (dry) and calcalkaline (wet) parental magmas were present. Petrologic evidence records the operation of complex, multi-stage processes including fractional crystallization, crustal assimilation, and magma mixing. Experimental evidence suggests that magmas were stored at 3 to 6 km depth prior to eruption, and that both wet and dry parental magmas were involved in generating the more silicic magmas. The broad distribution of eruptive events and the relative accessibility and good exposure of lavas, combined with physical and petrologic evidence for multiple and varied mafic inputs, has created an unusual opportunity to understand the workings of this large magmatic system. A combined total of more than 25 intrusive and extrusive events are indicated for late Holocene time. Plutonic inclusions, some with ages as young as Holocene, were also brought to the surface in five of the eruptions. All eruptions took place along northwest- to northeast-trending alignments of vents, reflecting the overall east-west extensional tectonic environment. The interaction of tectonism and volcanism is a dominant influence at this subduction-related volcano, located where the west edge of the extensional Basin and Range Province impinges on the Cascades arc. Ongoing subsidence focused at the central caldera has been documented along with geophysical evidence for a small magma body. This evidence, combined with the frequency of eruptive and intrusive activity in late Holocene time, an active geothermal system, and intermittent long-period seismic events indicate that the volcano is likely to erupt again.

California↗
USGS2000

Hydrologic and geologic characteristics of the Yucca Mountain site relevant to the performance of a potential repository

Yucca Mountain, located ~100 mi northwest of Las Vegas, Nevada, has been designated by Congress as a site to be characterized for a potential mined geologic repository for high-level radioactive waste. This field trip will examine the regional geologic and hydrologic setting for Yucca Mountain, as well as specific results of the site characterization program. The first day focuses on the regional setting with emphasis on current and paleo hydrology, which are both of critical concern for predicting future performance of a potential repository. Morning stops will be southern Nevada and afternoon stops will be in Death Valley. The second day will be spent at Yucca Mountain. The field trip will visit the underground testing sites in the "Exploratory Studies Facility" and the "Busted Butte Unsaturated Zone Transport Field Test" plus several surface-based testing sites. Much of the work at the site has concentrated on studies of the unsaturated zone, an element of the hydrologic system that historically has received little attention. Discussions during the second day will compromise selected topics of Yucca Mountain geology, hydrology and geochemistry and will include the probabilistic volcanic hazard analysis and the seismicity and seismic hazard in the Yucca Mountain area. Evening discussions will address modeling of regional groundwater flow, the results of recent hydrologic studies by the Nye County Nuclear Waste Program Office, and the relationship of the geology and hydrology of Yucca Mountain to the performance of a potential repository. Day 3 will examine the geologic framework and hydrology of the Pahute Mesa-Oasis Valley Groundwater Basin and then will continue to Reno via Hawthorne, Nevada and the Walker Lake area.

Nevada↗
USGS2007

State of the art and progress in the earthquake early warning system in Taiwan

We report here the recent progress and future development of real-time seismic monitoring in Taiwan, especially on earthquake early warning system (EWS) developed at the Central Weather Bureau (CWB), using the telemetered signals from strong-motion instruments. Utilizing a quick magnitude determination based on the first 10 sec of signals from a virtual and sub-network which is configured automatically, we were able to reduce the earthquake rapid reporting time to about 30 sec or less. This represents a significant step towards a more realistic earthquake early warning capability. This early warning system has been in operation at CWB since 2002. Comprehensive earthquake reports have been issued mostly in less than 30 sec, with an average of about 22 sec from the origin time. At 3 km/sec for a typical crustal shear-wave velocity, the present operation is not useful if an earthquake occurs less than about 70 km from a city, but the lead time will increase to more than 10 sec for cities at distances greater than 100 km from the earthquake source. In the latter case, a lead time of several seconds will allow pre-programmed emergency response to take place prior to the arrival of strong ground shaking. In order to offer earlier warning within an epicentral distance of less than 70 km, a τ c and Pd method was experimented. We used the Taiwan Strong-Motion Instrumentation Program (TSMIP) accelerograms recorded within epicentral distances of less than 30 km from Mw > 5.0 crustal earthquakes. This method uses the first 3-sec length records from the onset of P-waves and could issue an on-site early warning within 10 sec after the event origin time, reducing the radius of the blind zone from 70 to 25 km from the epicenter.

Book chapter↗
USGS1997

Continuous monitoring of surface deformation at Long Valley Caldera, California, with GPS

Continuous Global Positioning System (GPS) measurements at Long Valley Caldera, an active volcanic region in east central California, have been made on the south side of the resurgent dome since early 1993. A site on the north side of the dome was added in late 1994. Special adaptations for autonomous operation in remote regions and enhanced vertical precision were made. The data record ongoing volcanic deformation consistent with uplift and expansion of the surface above a shallow magma chamber. Measurement precisions (1 standard error) for “absolute” position coordinates, i.e., relative to a global reference frame, are 3–4 mm (north), 5–6 mm (east), and 10–12 mm (vertical) using 24 hour solutions. Corresponding velocity uncertainties for a 12 month period are about 2 mm/yr in the horizontal components and 3–4 mm/yr in the vertical component. High precision can also be achieved for relative position coordinates on short (less than 10 km) baselines using broadcast ephemerides and observing times as short as 3 hours, even when data are processed rapidly on site. Comparison of baseline length changes across the resurgent dome between the two GPS sites and corresponding two-color electronic distance measurements indicates similar extension rates within error (∼2 mm/yr) once we account for a random walk noise component in both systems that may reflect spurious monument motion. Both data sets suggest a pause in deformation for a 3.5 month period in mid-1995, when the extension rate across the dome decreased essentially to zero. Three dimensional positioning data from the two GPS stations suggest a depth (5.8±1.6 km) and location (west side of the resurgent dome) of a major inflation center, in agreement with other geodetic techniques, near the top of a magma chamber inferred from seismic data. GPS systems similar to those installed at Long Valley can provide a practical method for near real-time monitoring and hazard assessment on many active volcanoes.

Journal of Geophysical Research B: Solid Earth↗
USGS2004

Flow path of the 1993 Hokkaido-Nansei-oki earthquake seismoturbidite, suthern margin of the Japan sea north basin, inferred from anisotropy of magnetic susceptibility

A magnetic fabric analysis has been carried out on standard cube samples from one gravity and three multiple cores extracted from the Shiribeshi trough and Okushiri basin in the southern margin of the Japan sea north basin. It is aimed at tracing the flow path of turbidites that are assumed to have deposited in response to the 1993 Hokkaido-Nansei-oki earthquake. Magnetic remanence was used for reorientation to the geographic coordinates. Magnetomineralogical investigations including low-temperature magnetometry, magnetic hysteresis loops and isothermal remanent magnetization (IRM) acquisition experiments indicate that pseudosingle domain to multidomain magnetite is the principal magnetic carrier and is, therefore, capable of providing reliable anisotropy of magnetic susceptibility (AMS) palaeocurrent direction estimates. A well-developed near-horizontal magnetic foliation and minimum susceptibility axes lying close to vertical are recorded at all sites reflecting an original depositional fabric. Clearly defined magnetic lineation was observed at all sites and is considered to reflect the palaeocurrent direction. Down-core changes of susceptibility and key AMS parameters show good correspondence to occurrences of turbidite layers marking the increase of input of influx materials. In agreement with results from recent marine surveys and IZANAGI side-scan sonar images, an NNE transportation trend has been estimated for sediments at sites from the Shiribeshi trough with a possible depositing path initiating from the slope bounding the south and southeastern margin down to the trough floor. Similarly, a SSE palaeocurrent direction has been estimated for sediments from the Okushiri basin with evidence for a relatively strong transporting current flowing through the canyons along the steep slope bounding the north and northeastern margins of the basin. The present results agree with the view that slope failure is the most probable mechanism for the down-slope transport of the sand from the shelves and upper slopes down to floors of basins and troughs in the southern margin of the Japan sea north basin. They further support the ongoing assumption that the 1993 Hokkaido-Nansei-oki and other strong historical earthquakes together with associated tsunamis are the principal triggering forces for the down-slope mass gravitational transport and formation of turbidites in this seismically active area. ?? 2004 RAS.

Geophysical Journal International↗
USGS1985

Seismicity map of the State of Montana

This map is one of a series of seismicity maps produced by the U. S. Geological Survey that show earthquake data of individual states or groups of states at the scale of 1:1,000,000. This map shows only those earthquakes with epicenters located within the boundaries of Montana, even though earthquakes in bordering states or countries may have been felt or may have caused damage in Montana. The data in table 1 were used to compile the seismicity map; these data are a corrected, expanded, and updated (through 1981) version of the data used by Algermissen (1969) for a study of seismic risk in the United States. The locations and intensities of some earthquakes were revised and intensities were assigned where none had been before. Many earthquakes were added to the original list from new data sources as well as from some old data sources that had not been previously used. No earthquakes with magnitudes greater than 2.5 were located in Montana during 1981. The data in table 1 represent best estimates of the location of the epicenter, magnitude, and intensity of each earthquake on the basis of historical and current information. Some of the aftershocks from large earthquakes are listed, but not all, especially for earthquakes that occurred before seismic instruments were universally used. Special criteria used in compiling the list of earthquake in the State of Montana include the following: (1) All earthquakes with epicenters along the Montana-Wyoming border with a latitude of 45° N are listed in Montana. (2) Aftershocks of the 1925 and 1935 earthquakes were assigned the same geographic locations as the main shocks. (3) Instrumental epicenters for the 1959 Hebgen Lake earthquake and its aftershocks were 1ocated in Idaho, Montana, and Wyoming; only the ones located in Montana are included on this map. All non-instrumental locations were given the location of the main shock with an accuracy code that includes the community reporting the maximum intensity. The latitude and longitude coordinates of each epicenter were rounded to the nearest tenth of a degree and sorted so that all identical locations were grouped and counted. These locations are represented on the map by a triangle. The number of earthquakes at each location is shown on the map by the number to the right of the triangle. A Roman numeral to the left of a triangle is the maximum Modified Mercalli intensity (Wood and Neumann, 1931) of all earthquakes at that geographic location. The absence of an intensity value indicates that no intensities have been assigned to earthquakes at that location. The year shown below each triangle is the latest year for which the maximum intensity was recorded.

Montana↗
USGS2001

The Kiowa core, a continuous drill core through the Denver Basin bedrock aquifers at Kiowa, Elbert County, Colorado

The Kiowa core was obtained as a component of the Denver Basin Project, a cooperative research effort to study the evolution of the Denver Basin, Colorado. The Kiowa core provides a virtually continuous stratigraphic record of the Upper Cretaceous and lower Tertiary strata of the Denver Basin. The upper portion of the core recovered strata conventionally referred to as the Arapahoe and Denver Formations and the Dawson Arkose. A prominent unconformity marked by a mature paleosol breaks these strata into two unconformity-bounded sequences; the lower sequence is termed Dl and the upper sequence, D2. Beneath these units and also penetrated by the core occur the Laramie Formation, Fox Hills Sandstone, and Pierre Shale. The site for coring was selected in order to obtain fine-grained strata suitable for both palynological and paleomagnetic analyses. The coring effort recovered 93 percent of the 2,256 ft of rock penetrated, resulting in a nearly continuous record of the sedimentary rocks recording the retreat of the Cretaceous Interior Seaway and the subsequent uplift of the Front Range portion of the Rocky Mountains. Palynological data constrain the Cretaceous-Tertiary boundary to a depth between 878 and 880 ft in the core. The palynological data also serve to bracket the age of the paleosol marking the unconformity between the Dl and D2 sequences to between middle Paleocene and earliest Eocene. The paleomagnetic data are interpreted to represent polarity intervals ranging from polarity subchrons 31r to 28n and polarity subchron 24r. Hydrologic analyses indicate variable aquifer characteristics across the State-defined bedrock aquifers. Individual aquifer units exhibit generally lower water-yield potential than was identified to the west in a core drilled by the U.S. Geological Survey (USGS) in 1987 at Castle Pines, Colorado. Downhole temperature measurements indicate a normal geothermal gradient of 30°C/ km. Perturbations of the gradient may represent active fluid flow through the aquifers penetrated by the core. Petrographic examination of the cored sandstone and mudstone units document both the clay-rich character of the paleosol series marking the boundary between the Dl and D2 sequences, and variation in sandstone composition with depth. The lower sequence (Dl) is characterized by litharenites with a significant volcaniclastic component, while the upper sequence (D2) is more arkosic. Extensive lignite beds occur in Dl in the cored interval and these appear as strong reflectors on the seismic line that passes near the core hole. A set of electric logs, core descriptions, and derived data sets accompany this report.

Colorado↗
USGS1979

Initiation and development of the southern California uplift along its northern margin

Analysis of three first-order leveling lines that traverse the White Wolf fault (site of the 1952 M = 7.7 earthquake), each resurveyed nine times between 1926 and 1974, reveals probable preseismic tilting, major coseismic movements, and a spatial association between these movements and the subsequently recognized southern California uplift. In examining the vertical control record, we have both searched for evidence of systematic errors and excluded from consideration portions of the lines contaminated by subsurface fluid and gas extraction. Movements have been referred to an invariant datum based on the 1926 position of tidal BM 8 in San Pedro, corrected for subsequent eustatic sea-level change. An 8 μrad up-to-the-north preseismic tilt (6 cm/7.5 km) was apparently recorded on two adjacent line segments within 10 km of the 1952 epicenter between 1942 and 1947. It is possible, however, that this tilt was in part caused by extraction-induced subsidence at one of the six releveled benchmarks. Data also show evidence of episodic tilts that are not earthquake related. At the junction of the Garlock and San Andreas faults, for example, an ≥5 μrad up-to-the-north tilt (7.2 cm/≤16 km) took place between Lebec and Grapevine within three months during 1964. Comparison of the 1947 and 1953 surveys, which includes the coseismic interval, shows that the SW-fault end (nearest the epicenter) and the central fault reach sustained four times the uplift recorded at the NE end of the fault (+72 cm SW, +53 cm Central, +16 cm NE). A regional postseismic uplift of 4 cm extended ≥25 km to either side of the fault after the main event, from 1953 to 1956. An interval of relative quiescence followed at least through 1959, in which the elevation change did not exceed ±3 cm. The detailed pattern of aseismic uplift demonstrates that movement proceeded in space—time pulses: one half of the uplift at the SW-fault end and extending southward occurred between 1959 and 1961, one half of the uplift at the NE-fault end and extending eastward occurred between 1961 and 1965, while the central fault reach sustained successive pulses of subsidence, uplift, and collapse (−4 cm, 1953–1960; +7 cm, 1960–1965; −2 cm, 1965–1970). In addition, the number of aftershocks concentrated near the fault ends increased in the NE relative to the SW from 1952 to 1974. These observations suggest that the aseismic uplift may have migrated northeastward from 1959 to 1965 at an approximate rate of 7–16 km/yr. Evidence for a mechanical coupling between the earthquake and the subsequent aseismic uplift is equivocal. At both fault ends, the major NWbounding flexure or tilted front of the southern California uplift is spatially coincident with the coseismic flexure that preceded it. In addition, the postulated migration of vertical deformation is similar to the 1952 seismic event in which the rupture initiated at the SW end of the fault and then propagated to the NE-fault end. However, the spatial distribution of aseismic uplift, nearly identical at both fault ends and to the south and east, and near zero in the central fault reach, is distinctly different from the nonuniform and localized coseismic deformation.

California↗
USGS1982

Prediction of earthquake response spectra

We have developed empirical equations for predicting earthquake response spectra in terms of magnitude, distance, and site conditions, using a two-stage regression method similar to the one we used previously for peak horizontal acceleration and velocity. We analyzed horizontal pseudo-velocity response at 5 percent damping for 64 records of 12 shallow earthquakes in Western North America, including the recent Coyote Lake and Imperial Valley, California, earthquakes. We developed predictive equations for 12 different periods between 0.1 and 4.0 s, both for the larger of two horizontal components and for the random horizontal component. The resulting spectra show amplification at soil sites compared to rock sites for periods greater than or equal to 0.3 s, with maximum amplification exceeding a factor of 2 at 2.0 s. For periods less than 0.3 s there is slight deamplification at the soil sites. These results are generally consistent with those of several earlier studies. A particularly significant aspect of the predicted spectra is the change of shape with magnitude (confirming earlier results by McGuire and by Irifunac and Anderson). This result indicates that the conventional practice of scaling a constant spectral shape by peak acceleration will not give accurate answers. The Newmark and Hall method of spectral scaling, using both peak acceleration and peak velocity, largely avoids this error. Comparison of our spectra with the Nuclear Regulatory Commission's Regulatory Guide 1.60 spectrum anchored at the same value at 0.1 s shows that the Regulatory Guide 1.60 spectrum is exceeded at soil sites for a magnitude of 7.5 at all distances for periods greater than about 0.5 s. Comparison of our spectra for soil sites with the corresponding ATC-3 curve of lateral design force coefficient for the highest seismic zone indicates that the ATC-3 curve is exceeded within about 7 km of a magnitude 6.5 earthquake and within about 15 km of a magnitude 7.5 event. The amount by which it is exceeded for the 7.5 event is largest in the period range from 0.5 to 2.0 s.

Open-File Report↗
USGS2010

The North American Midcontinent rift beneath Lake Superior from GLIMPCE seismic reflection profiling

The Midcontinent rift system is a 1.1-b.y.-old structure extending from Kansas, through the Lake Superior region, and into southern Michigan. The rift is filled with thick sequences of basaltic volcanic rocks and clastic sediments. For most of its extent it is buried beneath Paleozoic rocks but can be traced by its strong gravity and magnetic anomalies. The rocks of the rift system are exposed only in the Lake Superior region and comprise the Keweenawan Supergroup. Much of the geology of the Keweenawan is beneath Lake Superior and has only been inferred from potential field studies and seismic refraction studies and extrapolation from on-shore geology. Seismic reflection surveys by the Great Lakes International Multidisciplinary Program on Crustal Evolution in 1986 imaged much of the deep structure of the rift beneath the lake in detail. The reflection profiles across the rift reveal a deep, asymmetrical central graben whose existence and magnitude was not previously documented. They show that, in addition to crustal sagging documented by previous investigations, normal faulting played a major role in subsidence of the axial region of the rift. A sequence of volcanic and sedimentary rocks, in places greater than 30 km thick, fills the graben. Thinner volcanic and sedimentary units lie on broad flanks of the rift outside of the graben. Near the axis, the prerift crust is thinned to about one fourth of its original thickness, apparently by a combination of low-angle extensional faulting and ductile stretching or distributed shear. The sense of asymmetry of the central graben changes along the trend of the rift, documenting the segmented nature of the structure and suggesting the existence of accommodation zones between the segments. The location of the accommodation zones is inferred from abrupt disruptions in the Bouguer gravity signature of the rift. Uplift of the central graben occurred when the original graben-bounding normal faults were reactivated as high-angle reverse faults with throws of 5 km or more in places. The Midcontinent rift has some striking similarities to some younger passive continental margins. We propose that it preserves a record of nearly complete continental separation which, had it not been arrested, would have created a Middle Proterozoic ocean basin.

Lake Superior↗
USGS2005

Evidence for New Madrid earthquakes in A.D. 300 and 2350 B.C

Six episodes of earthquake-induced liquefaction are associated with soil horizons containing artifacts of the Late Archaic (3000-500 B.C.) and Early to Middle Woodland (500 B.C.-A.D. 400) cultural periods at the Burkett archaeological site in the northern part of the New Madrid seismic zone, where little information about prehistoric earthquakes has been available. Radiocarbon dating of organic material and analysis of artifacts are used to estimate the ages of the liquefaction features and times of the causative earthquakes. The most recent episode of liquefaction occurred after A.D. 1670, produced small sand dikes, and is probably related to the 1895 Charleston, Missouri earthquake. The preceding episode struck the area in A.D. 300 ± 200 years and generated a sand blow that contains Late Woodland artifacts and buries an Early to Middle Woodland cultural horizon. Four older episodes of liquefaction occurred in 2350 B.C. ± 200 years and may have been produced by a sequence of closely timed earthquakes. The four earlier episodes produced graben structures, sand dikes, and associated sand blows on which a cultural mound was constructed. The Burkett liquefaction features that formed about 2350 B.C. and A.D. 300 are relatively large and similar in age to other liquefaction features in northeastern Arkansas and southeastern Missouri, respectively. If the prehistoric features at the Burkett site and those of similar age elsewhere in the region are the result of the same earthquakes, then this suggests that they were similar in size to the three largest (M 7-8) 1811-1812 New Madrid earthquakes. A New Madrid-type earthquake in A.D. 300 ± 200 years would support an average recurrence time of 500 years. Although this study extends the earthquake chronology back to 2500 B.C., it is uncertain that the record of New Madrid events is complete for the period between 2350 B.C. and A.D. 300. As demonstrated by this study, information about other prehistoric earthquakes may be buried beneath fluvial deposits of the Mississippi River Valley.

Arkansas, Illinois, Kentucky, Missouri, Tennessee↗