Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Earthquake Spectra”

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

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources
USGS2017

Trimming a hazard logic tree with a new model-order-reduction technique

The size of the logic tree within the Uniform California Earthquake Rupture Forecast Version 3, Time-Dependent (UCERF3-TD) model can challenge risk analyses of large portfolios. An insurer or catastrophe risk modeler concerned with losses to a California portfolio might have to evaluate a portfolio 57,600 times to estimate risk in light of the hazard possibility space. Which branches of the logic tree matter most, and which can one ignore? We employed two model-order-reduction techniques to simplify the model. We sought a subset of parameters that must vary, and the specific fixed values for the remaining parameters, to produce approximately the same loss distribution as the original model. The techniques are (1) a tornado-diagram approach we employed previously for UCERF2, and (2) an apparently novel probabilistic sensitivity approach that seems better suited to functions of nominal random variables. The new approach produces a reduced-order model with only 60 of the original 57,600 leaves. One can use the results to reduce computational effort in loss analyses by orders of magnitude.

Earthquake Spectra↗
USGS2016

Responses of two tall buildings in Tokyo, Japan, before, during, and after the M9.0 Tohoku earthquake of 11 March 2011

The 11 March 2011 M 9.0 Tohoku earthquake generated significant long duration shaking that propagated hundreds of kilometers from the epicenter and affected urban areas throughout much of Honshu. Recorded responses of tall buildings at several hundred km from the epicenter of the main shock and other events show tall buildings were affected by long-period motions of events at distant sources. This study presents behavioral aspects of 29-story and 30-story neighboring buildings in the Shinjuku area of Tokyo, Japan, as inferred from records retrieved from a sparse array of accelerometers deployed in the superstructures, at ground and 100 m below the ground level over a time interval covering before, during, and after the main shock. Such long-period effects are common in several regions of Japan as well as in the United States and in other seismically active countries. Permanent shifts in fundamental frequencies are observed. Drift ratios indicate possible structural nonlinear behavior occurred during the main shock. The need to consider risks to built environments from distant sources, including those in neighboring countries, is emphasized.

Tokyo↗
USGS2002

GPS in pioneering dynamic monitoring of long-period structures

Global Positioning System (GPS) technology with 10-20-Hz sampling rates allows scientifically justified dynamic measurements of relative displacements of long-period structures. The displacement response of a simulated tall building in real time and permanent deployment of GPS units at the roof of a building are described. To the authors' best knowledge, this is the first permanent deployment of GPS units (in the world) for continuous dynamic monitoring of a tall building. Data recorded from the building during a windy day is analyzed to determine the structural characteristics. When recorded during extreme motions caused by earthquakes and strong winds, such measurements can be used to compute average drift ratios and changes in dynamic characteristics, and therefore can be used by engineers and building owners or managers to assess the structural integrity and performance by establishing pre-established thresholds. Such information can be used to secure public safety and/or take steps to improve the performance of the building.

Earthquake Spectra↗
USGS2003

Identification of site frequencies from building records

A simple procedure to identify site frequencies using earthquake response records from roofs and basements of buildings is presented. For this purpose, data from five different buildings are analyzed using only spectral analyses techniques. Additional data such as free-field records in close proximity to the buildings and site characterization data are also used to estimate site frequencies and thereby to provide convincing evidence and confirmation of the site frequencies inferred from the building records. Furthermore, simple code-formula is used to calculate site frequencies and compare them with the identified site frequencies from records. Results show that the simple procedure is effective in identification of site frequencies and provides relatively reliable estimates of site frequencies when compared with other methods. Therefore the simple procedure for estimating site frequencies using earthquake records can be useful in adding to the database of site frequencies. Such databases can be used to better estimate site frequencies of those sites with similar geological structures.

Earthquake Spectra↗
USGS2003

A methodology for probabilistic fault displacement hazard analysis (PFDHA)

We present a methodology for conducting a site-specific probabilistic analysis of fault displacement hazard. Two approaches are outlined. The first relates the occurrence of fault displacement at or near the ground surface to the occurrence of earthquakes in the same manner as is done in a standard probabilistic seismic hazard analysis (PSHA) for ground shaking. The methodology for this approach is taken directly from PSHA methodology with the ground-motion attenuation function replaced by a fault displacement attenuation function. In the second approach, the rate of displacement events and the distribution for fault displacement are derived directly from the characteristics of the faults or geologic features at the site of interest. The methodology for probabilistic fault displacement hazard analysis (PFDHA) was developed for a normal faulting environment and the probability distributions we present may have general application in similar tectonic regions. In addition, the general methodology is applicable to any region and we indicate the type of data needed to apply the methodology elsewhere.

Earthquake Spectra↗
USGS1989

Seismology

No abstract available.

Caucasus Mountains, Lesser Caucasus highlands↗
USGS1989

Surface faulting: A preliminary view

This description of surface faulting near Spitak, Armenia, is based on a field inspection made December 22-26, 1988. The surface rupture west of Spitak, displacement of the ground surface, pre-earthquake surface expressions of the fault, and photolineaments in landsat images are described and surface faulting is compared to aftershocks. It is concluded that the 2 meters of maximum surface displacement fits well within the range of reliably measured maximum surface offsets for historic reverse and oblique-reverse faulting events throughout the world. By contrast, the presently known length of surface rupture near Spitak, between 8 and 13 km, is shorter than any other reverse or oblique-reverse event of magnitude greater than 6.0. This may be a reason to suppose that additional surface rupture might remain unmapped.

Earthquake Spectra↗
USGS1989

Effect of site conditions on ground motion and damage

Results of seismologic studies conducted by the U.S. reconnaissance team in conjunction with Soviet colleagues following the tragic earthquakes of December 7, 1988, suggest that site conditions may have been a major factor in contributing to increased damage levels in Leninakan. As the potential severity of these effects in Leninakan had not been previously identified, this chapter presents results intended to provide a preliminary quantification of these effects on both damage and levels of ground motion observed in Leninakan. The article describes the damage distribution geologic setting, ground motion amplification in Leninakan, including analog amplifications and spectral amplifications. Preliminary model estimates for site response are presented. It is concluded that ground motion amplification in the 0.5-2.5-second period range was a major contributing factor to increased damage in Leninakan as compared with Kirovakan. Leninakan is located on thick water saturated alluvial deposits.

Shirak↗
USGS1988

The Whittier Narrows, California earthquake of October 1, 1987: Preliminary assessment of strong ground motion records

More than 250 strong-motion accelerograph stations were triggered by the Whittier Narrows, California, earthquake of 1 October 1987. Considering the number of multichannel structural stations in the area of strong shaking, this set of records is one of the more significant in history. Three networks, operated by the U.S. Geological Survey, the California Division of Mines and Geology, and the University of Southern California produced the majority of the records. The excellent performance of the instruments in these and the smaller arrays is attributable to the quality of the maintenance programs and their funding and personnel requirements. Readiness for a magnitude 8 event is directly related to these maintenance programs. Prior to computer analysis of the analog film records, a number of important structural resonant modes can be identified, and frequencies and simple mode shapes have been scaled. The structural records form a basic performance measurement for comparison with larger earthquake response in the future.

California↗
USGS1989

Seismic response of a large-span roof diaphragm

Records obtained from the West Valley College Gymnasium in Saratoga, California during the 1984 Morgan Hill earthquake are used to study the dynamic behavior of the overall gymnasium as well as its flexible disaphragm. The ground-level motions recorded in the two orthogonal axes of the structure differ considerably in peak acceleration and amplify by approximately 1.5 times at the roof edges and by 4-5 times at the center of the diaphragm. The diaphragm responds with a frequency of approximately 4 Hz in both orthogonal axes. A simple finite-element model is used to match the fundamental frequency of the diaphragm with that from the records. Using this model and the ground-level motions as input, the diaphragm center displacements are calculated by varying the structural damping. Best comparisons are obtained for 5% damping. These results are discussed in terms of the code provisions.

Earthquake Spectra↗
USGS1989

Seismic velocities and attenuation from borehole measurements near the Parkfield prediction zone, Central California

Shear (S)- and compressional (P)- wave velocities were measured to a depth of 195 m in a borehole near the San Andreas fault where a recurrence of a moderate Parkfield earthquake is predicted. S-wave velocities determined from orthogonal directions of the S-wave source show velocity differences of approximately 20 percent. An average shear-wave Q of 4 was determined in relatively unconsolidated sands and gravels of the Paso Robles Formation in the depth interval 57.5-102.5 m.

Earthquake Spectra↗
USGS1990

Perspectives on the international decade for natural disaster reduction

Disaster preparedness and disaster mitigation are the goals of nations throughout the world during the 1990's. The United States will lead this cooperative effort and marshall its national resources to reduce the disaster potential of earthquakes, floods, windstorms, landslides, volcanic eruptions, tsunamis, and wildfires. These natural hazards cause annual losses of approximately $10 billion in the United States and many times that throughout the world. The type and severity of the hazard varies from State-to-State in the United States. All States are at risk from flooding from sources such as precipitation, snowmelt, thunderstorms, and, along the coast, the storm surges generated in hurricanes. No State is free from the potential impacts of ground shaking induced by earthquakes. The goal of the Decade is to keep such occurrences in the future from being disasters.

Earthquake Spectra↗
USGS1993

Pilot studies of seismic hazard and risk in North Sulawesi Province, Indonesia

Earthquake ground motions in North Sulawesi on soft soil that have a 90% probability of not been exceeded in 560 years are estimated to be 0.63 g (63% of the acceleration of gravity) at Palu, 0.31 g at Gorontalo, and 0.27 g at Manado. Estimated ground motions for rock conditions for the same probability level and exposure time are 56% of those for soft soil. The hazard estimates are obtained from seismic sources that model the earthquake potential to a depth of 100 km beneath northern and central Sulawesi and include the Palu fault zone of western Sulawesi, the North Sulawesi subduction zone, and the southern most segment of the Sangihe subduction zone beneath the Molucca Sea. An attenuation relation based on Japanese strong-motion data and considered appropriate for subduction environments of the western Pacific was used in determination of ground motions. Following the 18 April 1990 North Sulawesi earthquake (Ms 7.3) a seismic hazard and risk assessment was carried out. -from Authors

Earthquake Spectra↗
USGS1997

Models and methods to characterize site amplification from a pair of records

The paper presents a tutorial review of the models and methods that are used to characterize site amplification from the pairs of rock- and soil-site records, and introduces some new techniques with better theoretical foundations. The models and methods discussed include spectral and cross-spectral ratios, spectral ratios for downhole records, response spectral ratios, constant amplification factors, parametric models, physical models, and time-varying filters. An extensive analytical and numerical error analysis of spectral and cross-spectral ratios shows that probabilistically cross-spectral ratios give more reliable estimates of site amplification. Spectral ratios should not be used to determine site amplification from downhole-surface recording pairs because of the feedback in the downhole sensor. Response spectral ratios are appropriate for low frequencies, but overestimate the amplification at high frequencies. The best method to be used depends on how much precision is required in the estimates.

Earthquake Spectra↗
USGS1999

TriNet "ShakeMaps": Rapid generation of peak ground motion and intensity maps for earthquakes in southern California

Rapid (3-5 minutes) generation of maps of instrumental ground-motion and shaking intensity is accomplished through advances in real-time seismographic data acquisition combined with newly developed relationships between recorded ground-motion parameters and expected shaking intensity values. Estimation of shaking over the entire regional extent of southern California is obtained by the spatial interpolation of the measured ground motions with geologically based frequency and amplitude-dependent site corrections. Production of the maps is automatic, triggered by any significant earthquake in southern California. Maps are now made available within several minutes of the earthquake for public and scientific consumption via the World Wide Web; they will be made available with dedicated communications for emergency response agencies and critical users.

California↗