Archive for the ‘strong ground motion’ Category

Strong-motion records from the magnitude 5.1 Mw earthquake which occurred 1 km South of La Habra in Southern California, at 9:09 pm on March 28, 2014, are available from the Center for Engineering Strong Motion Data (CESMD).

This earthquake was preceded by two foreshocks, the larger of M3.6 at 8:03 pm and several aftershocks. According to the Southern California Seismic Network, this sequence could be associated with the Puente Hills thrust (PHT). The PHT is a blind thrust fault that extends from this region to the north and west towards the City of Los Angeles. This fault has also been associated with the M5.9 1987 Oct. 1 Whittier Narrows earthquake.

Strong-Motion data from more than 270 structural and ground response stations of the California Integrated Seismic Network stations (CGS, USGS and SCSN) are available at this time for view and download. The largest peak ground acceleration of 0.71g was recorded at epicentral distance of about 5 km, in the city of Brea. As of this date, records from 16 stations recorded the earthquake with peak ground acceleration larger than 10%g, and 7 stations have recorded this earthquake within about 10 km from the epicenter.

CESMD staff at USGS and CGS

In late May, 2013, PEER’s NGA-West2 project, the second and final phase of the Next Generation Attenuation relationships for shallow crustal earthquakes in active tectonic regions (Western U.S.A.), released a series of reports of its work in developing Ground Motion Prediction Equations (GMPE). Updated and expanded GMPE procedures (from the original 2008 models) are available, data files used in various research components of NGA-West2 are documented (See: Timothy D. Ancheta et al, PEER-2013/03), and the earthquake ground motion data have been made public as the NGA-West2 database “flat files”.

The NGA-West2 project database expands on the current PEER NGA ground-motion database to include worldwide ground-motion data recorded from shallow crustal earthquakes in active tectonic regions, post-2003. Events are considered shallow crustal if they occur within the continental lithosphere. The region used to collect shallow events is considered “tectonically active” if the earthquake is not located in a stable continental region (SCR), within a subducting slab or on the interface between the slab and the continental lithosphere; typically these events are near a plate boundary. Additionally, events were not excluded if they occurred in close proximity (time and space) with a previous event.

Peak ground accelerations normalized to a reference Vs30 of 500 m/sec for the 1992 Big Bear earthquake compared with the Abrahamson and Silva 2008 GMPE for both mainshocks and aftershocks.

The new data set comprised 21,539 recordings obtained during earthquakes with magnitudes ranging from 3 to 7.9, recorded at distances ranging from 0.2 km to over 300 km, and for recording stations with Vs30 (time-averaged shear-wave velocity in the top 30 m at the recording sites) ranging from 100 to 2000 m/sec. These data spanned the larger magnitude range (M = 4.5 to 7.9) and the small magnitude range. Thousands of ground motions recorded from small-to-moderate magnitude (with M = 3 to 5.5) events in California were also added. The new database includes uniformly processed time series as well as response spectral ordinates for 111 periods ranging from 0.01 to 20 sec and with 11 different damping ratios.

The quality of the strong motion database and of the subsets selected for closer study by each GMPE model team are critical for wider application of the NGA-West2 GMPE. (See: Iztok Peruš and Peter Fajfar. How Reliable are the Ground Motion Prediction Equations? SMiRT 20 – August 2009; for discussion of some other key issues for wider application). The recent history of earthquake ground motion prediction models has been well documented by John Douglas (See: ESEE 01-1 A comprehensive worldwide summary of strong-motion attenuation relationships for peak ground acceleration and spectral ordinates (1969 to 2000); BRGM/RP-56187-FR Further errata of and additions to ‘Ground motion estimation equations 1964 – 2003′ – final report and PEER-2011/102/Ground-motion prediction equations 1964 – 2010.

Strong Ground Motion – Selected and Simulated

Posted by cdj On October - 25 - 2011

In a project on earthquake strong ground motion selection and scaling for the analysis of transportation structural and geotechnical systems at locations throughout California (or regions where seismic hazard is dominated by mid-to-large-magnitude crustal earthquakes at near-to-moderate distances) PEER-funded researchers, Jack Baker et al, developed a new selection algorithm that allows the user to select a set of ground motions whose response spectra match a target mean and variance. The research is outlined in PEER Report 2011/03 – New Ground Motion Selection Procedures and Selected Motions for the PEER Transportation Research Program by Jack W. Baker, Ting Lin, Shrey K. Shahi, and Nirmal Jayaram. The algorithm is based on the empirically verified observation that the set of logarithmic spectral accelerations at various periods is a random vector that follows a multivariate normal distribution (Jayaram and Baker 2008). This algorithm was used to generate five sample sets of standardized earthquake strong ground motion records from the PEER Next Generation Attenuation (NGA) Project ground motion library of 3,551 multi-component ground motions from 173 earthquakes ranging in magnitudes from 4.3 to 7.9, primarily from shallow crustal earthquakes in seismically active regions of the world. The following five suites of ground motions representing different magnitudes, soil conditions, distances from rupture, etc. are available for download from the PEER Ground Motion for Transportation pages:

    Set #1a: Broad-band ground motions (M = 7, R = 10 km, soil site)
    Set #1b: Broad-band ground motions (M = 6, R = 25 km, soil site)
    Set #2: Broad-band ground motions (M = 7, R = 10 km, rock site)
    Set #3: Pulse-like ground motions
    Set #4: Site-specific ground motions for Oakland consists of ground motions selected to match the uniform hazard spectrum and associated causal events for a site in Oakland, California. Forty ground motions are provided to represent the ground motion hazard at each of three hazard levels (2%, 10% and 50% probabilities of exceedance in 50 years).

For situations where recorded strong ground motions for specified earthquake and site characteristics are limited in number, synthetic ground motions that can supplement or supplant recorded motions for analysis for a wide spectrum of earthquake and site characteristics can be developed stochastically. In another PEER-funded, transportation systems study, by identifying the parameters of the stochastic model for a large sample of recorded accelerograms drawn from the NGA library, predictive equations are developed that empirically relate the model parameters to a set of earthquake and site characteristics. Using these equations, for specified earthquake and site characteristics, sets of the model parameters are generated that are used in the stochastic model to generate an ensemble of synthetic ground motions. The resulting synthetic accelerations, as well as corresponding velocity and displacement time-histories, capture the main features of real earthquake ground motions, including the evolving intensity, duration, spectral content, natural variability, and peak values. Furthermore, the statistics of their resulting elastic response spectra, i.e., the median and logarithmic standard deviation, closely agree with values predicted by the NGA ground motion prediction equations. The research is documented in PEER 2010/02 – Stochastic Modeling and Simulation of Ground Motions for Performance-Based Earthquake Engineering by Sanaz Rezaeian and Armen Der Kiureghian.

Probabilistic Ground Motion Maps – 2009

Posted by cdj On September - 30 - 2011

This short, Earthquake Spectra opinion piece published in August, 2011 (Earthquake Spectra 27, pp. 927-937; doi:10.1193/1.3608001 – authored by an array of mostly west coast-based engineers and engineering seismologists) takes the view that the proposed, maximum-direction, ground motion definitions in the 2009 NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures can introduce an overly-conservative bias to design ground motions. The article concludes that, pending further research, the use of the existing USGS probabilistic ground motion maps combined with NEHRP site and risk factors represent the probabilistically most consistent basis currently available for evaluating design ground motions along the principal axes of structures.

Mineral, Virginia earthquake strong motion data

Posted by cdj On August - 25 - 2011

Looking for strong motion records from the rare Eastern U.S., Mineral, Virginia (Mw=5.8) earthquake of 23 August, 2011? The Center for Engineering Strong Motion Data (CESMD) has posted updated records here.
A concise account of the nuclear generating facilities in Virginia following the earthquake is provided by MIT nuclear science and engineering group which includes in its summary the observation, “…California is a disjointed geologic hodgepodge that dissipates seismic energy”… Makes one wonder on their view of Texas…

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