California Strong Motion Instrumentation Program Research Articles

Prediction for underground seismic intensity measures using conditional generative adversarial networks

With the escalating development and utilization of subterranean spaces, the seismic hazards faced by underground structures are progressively increasing. However, owing to the challenges associated with acquiring underground seismic data and historical seismic design norms, pertinent regulations and research in this domain are scarce. This study focused on three crucial intensity measures in the seismic design process of underground structures peak ground acceleration (PGA), peak ground velocity (PGV), and peak ground displacement (PGD). The research leverages seismic data obtained from the California Strong Motion Instrumentation Program (CSMIP) to train and evaluate a conditional generative adversarial network (CGAN) model. This model was employed to establish a multivariate joint conditional probability distribution among the intensity measures at varying depths, facilitating the stochastic prediction of shallow intensity measures. In contrast to empirical formulas, the CGAN model eliminates the need for a predefined equation structure and enables the simultaneous prediction of multiple intensity measures. The performance of the model was evaluated by comparing the predictive accuracy of the CGAN model and empirical fitting formulas across diverse site conditions and depth intervals using metrics such as relative error coefficients. It can be concluded that the proposed CGAN model can accurately predict shallow seismic intensity measures, and the predictions conform to a specific conditional distribution while retaining the stochastic nature of seismic motion. Compared with empirical formula models, the CGAN model exhibited an enhanced predictive capability.

Numerical modeling and validation of earthquake soil structure interaction: a 12-story building in Ventura, California

Presented is a validation study for high fidelity numerical modeling of earthquake soil structure interaction (ESSI) for a building, hotel structure in Ventura, California. A detailed finite element (FE) model of the ESSI system, featuring the 12-story concrete structure, pile group foundation, and underlying soil, is developed using the Real-ESSI Simulator (Jeremić et al., The Real-ESSI Simulator System 1988–2022, 2022a). The domain reduction method (DRM) (Bielak et al., Bulletin of the Seismological Society of America, 2003, 93(2), 817–824; Yoshimura et al., Bulletin of the Seismological Society of America, 2003, 93(2), 825–841) is used to apply seismic loads, in this case the 1994 Northridge earthquake motions. Direct comparison between simulation results and California Strong Motion Instrumentation Program (CSMIP) recordings shows a high level of agreement in acceleration and displacement responses at all instrumented locations. Sensitivity study on a number of modeling choices and analysis parameters is conducted to investigate controlling factors for the ESSI response. For example, the soil-structure interaction effect and structural damping ratios are shown to have significant influence on system dynamic response. In addition, the soil inelasticity is shown to be highly influenced by the magnitude of seismic motion. Both effects are important for validation as they contribute to sensitivity of response to parametric variability.

Evaluation of the Floor Acceleration Amplification Demand of Instrumented Buildings

The floor acceleration amplification (FAA) factor is one of the most critical parameters in computing the equivalent seismic force of nonstructural component (NC). To evaluate the heightwise FAA distribution profile, the recorded acceleration response of the instrumented buildings was analyzed using the California Strong Motion Instrumentation Program (CSMIP) database. The FAA demands for three groups of buildings consisting of reinforced concrete, steel, and masonry buildings were analyzed. In each group, the buildings were classified into four subgroups according to their heights. Parabolic distribution profiles were suggested that could envelop most of the FAA data, as demonstrated by the processed results. An earthquake experience-based importance factor was suggested in terms of the percentage of the enveloped records. The obtained FAAs at the roof were generally larger than those in other levels. The percentile distributions of the roof acceleration amplification (RAA) were computed. The results showed that the roof FAA was underestimated in ASCE 7-16. The magnitudes of the FAA and the RAA correlated to the fundamental period of the building, which was considered by classifying the buildings according to the period ranges. The RAA profile against the period was obtained from a regression analysis. The developed FAA profile is expected to be useful in the seismic design of NCs, and it is expected to be adopted in future code provisions.

2019 Ridgecrest Earthquake Reveals Areas of Los Angeles That Amplify Shaking of High-Rises

AbstractThe populace of Los Angeles, California, was startled by shaking from the M 7.1 earthquake that struck the city of Ridgecrest located 200 km to the north on 6 July 2019. Although the earthquake did not cause damage in Los Angeles, the experience in high-rise buildings was frightening in contrast to the shaking felt in short buildings. Observations from 560 ground-level accelerometers reveal large variations in shaking in the Los Angeles basin that occurred for more than 2 min. The observations come from the spatially dense Community Seismic Network (CSN), combined with the sparser Southern California Seismic Network and California Strong Motion Instrumentation Program networks. Site amplification factors for periods of 1, 3, 6, and 8 s are computed as the ratio of each station’s response spectral values combined for the two horizontal directions, relative to the average of three bedrock sites. Spatially coherent behavior in site amplification emerges for periods ≥3 s, and the maximum calculated site amplifications are the largest, by factors of 7, 10, and 8, respectively, for 3, 6, and 8 s periods. The dense CSN observations show that the long-period amplification is clearly, but only partially, correlated with the depth to basement. Sites with the largest amplifications for the long periods (≥3 s) are not close to the deepest portion of the basin. At 6 and 8 s periods, the maximum amplifications occur in the western part of the Los Angeles basin and in the south-central San Fernando Valley sedimentary basin. The observations suggest that the excitation of a hypothetical high-rise located in an area characterized by the largest site amplifications could be four times larger than in a downtown Los Angeles location.

Performance-based post-earthquake decision making for instrumented buildings

This paper develops a decision making framework for post-earthquake assessment of instrumented buildings in a manner consistent with performance-based design criteria. This framework is achieved by simultaneously combining and advancing existing knowledge from seismic structural health monitoring and performance-based earthquake engineering paradigms. The framework consists of (1) measurement, (2) uncertainty modeling, (3) dynamic response reconstruction, (4) damage estimation, and (5) performance-based assessment and decision making. In particular, the main objective is to reconstruct inter-story drifts with a probabilistic measure of exceeding performance-based acceptance limits and determine the post-earthquake re-occupancy classification of the instrumented building of interest. Since the proposed framework is probabilistic, the outcome can be used to obtain the probability of losses based on the defined decision variables and be integrated into a risk-based decision making process by city officials, building owners, and emergency managers. The framework is illustrated using data from the Van Nuys hotel testbed, a seven-story reinforced concrete building instrumented by the California Strong Motion Instrumentation Program (CSMIP Station 24386).

Geotechnical risk analyses and evaluation of design criteria of embankment dam systems

The integrity of the state and national system of embankment dams and levees is a crucial component in ensuring the safety of protected communities in any country. The failure of such systems due to natural or man-made hazards can have monumental repercussions, sometimes with dramatic and unanticipated consequences on human life, property and the economy of the states and the country. For highly seismic areas such as Southern California, it is critical to investigate and study the seismic response of embankment dams and levees for the afore mentioned reasons. While experimental studies of embankment dams under seismic loads is expensive, very time consuming, and limited, numerical studies usually suffer from lack of legitimate real data for verification of the developed models. However, organizations such as the California Strong Motion Instrumentation Program (CSMIP) instrument lifeline structures such as earth dams and levees with accelerometers and actively collect strong-motion data. The data obtained from CSMIP accelerometers is then processed by the Center for Engineering Strong Motion Data (CESMD) and made public for earthquake engineering applications. In this study, numerical models of existing earth embankment dams verified with site specific CESMD data are created in order to analyze their stability for a future earthquake, for post-earthquake response purposes. The seismic fragility of the modelled dams was assessed, providing insight for decision makers regarding priority areas important for matters such as maintenance, dam retrofit, or first-aid response locations for a hypothetical major earthquake. Society can benefit from increased awareness of the seismic response of the modelled structures and can be better prepared for a potential catastrophic seismic event.

Apparent Wave Velocity and Site Amplification at the California Strong Motion Instrumentation Program Carquinez Bridge Geotechnical Arrays during the 2014 M6.0 South Napa Earthquake

The Carquinez Bridge geotechnical arrays are operated by the California Strong Motion Instrumentation Program (CSMIP) and recorded a peak ground acceleration (PGA) of approximately 1.0g at ground surface during the 2014 South Napa earthquake. The recorded PGA was significantly larger than those at the nearby surface sites. This study considers surface and downhole recordings from the additional 28 earthquakes recorded at the same arrays to understand the effects of wave propagation and site response at these arrays. Several site response analyses are performed to understand soil nonlinearity using the observed ground accelerations during the 2014 South Napa sequence. Apparent shear wave velocities are calculated from downhole records, which show clear reduction as ground motion intensity increases. Empirical transfer functions (EFTs) are also calculated in which the resonance frequencies became lower during strong shaking during the 2014 South Napa main shock. The in-situ critical damping ratio appears to be frequency dependent in the soft clay deposits. Lower damping at frequencies greater than about 5 Hz may have contributed to the observed PGA at Array #1 during the main shock.

Evaluation of the Rayleigh damping model for buildings

Using damping ratios inferred from accelerations recorded during earthquakes in instrumented buildings in California this paper evaluates the Rayleigh damping model commonly used in seismic analysis of buildings. Damping ratios were obtained from 119 seismic responses, coming from 24 buildings, measured in 46 earthquakes over the past 25years by the California Strong Motion Instrumentation Program. All records were analyzed using a least-squares parametric system identification technique in the time domain. Using only damping ratios judged to be reliable, the variation of damping with modal frequencies is studied for all buildings. It is found that in 96% of the cases, modal damping ratios increase approximately linearly with frequency; showing that damping in buildings is best represented by using a model consisting of a constant damping ratio plus a stiffness-proportional damping ratio. No evidence was found to suggest that a mass-proportional model nor a combination of mass- and stiffness-proportional damping is appropriate. It is shown that the Rayleigh damping model, when used in combination with assumptions commonly used in engineering practice, typically leads to overestimations of mean peak floor accelerations, peak floor velocities, and interstory drift ratio demands with respect to those computed using the damping model inferred from the recorded data.

Correlation between Ground Motion and Building Response using California Earthquake Records

Using data from the California Strong Motion Instrumentation Program, we studied the relationship between building response and parameters describing the noxiousness of ground motion. According to vulnerability methods that use structural drift as damage criteria, we estimated the building response on the basis of the normalized relative roof displacement (NRRD), considered as damage criteria. The relationships between the NRRD and the intensity measures of the ground motion are developed using simulated annealing method. Grouping buildings by typology (defined according to their main construction material and height) reduces the variability of the building response. Furthermore, by combining IMs, the NRRD can be predicted more accurately by a building damage prediction equation. A functional form is thus proposed to estimate the NRRD for several building typologies, calibrated on the building responses recorded in California. This functional form can be used to obtain a fast and overall damage forecast after an earthquake.

Unusual Downhole and Surface Free‐Field Records Near the Carquinez Strait Bridges during the 24 August 2014Mw 6.0 South Napa, California, Earthquake

This paper reports the results of Part A of a study of the recorded strong‐motion accelerations at the well‐instrumented network of the two side‐by‐side parallel bridges over the Carquinez Strait during the 24 August 2014 ( M w 6.0) South Napa, California, earthquake that occurred at 03:20:44 Pacific Daylight Time (PDT) with epicentral coordinates 38.22° N, 122.31° W (http://earthquake.usgs.gov/earthquakes/eqarchives/poster/2014/20140824.php; last accessed October 2014). Both bridges and two boreholes were instrumented by the California Strong motion Instrumentation Program (CSMIP) of the California Geological Survey (CGS; Shakal et al. , 2014). A comprehensive comparison of several ground‐motion prediction equations as they relate to recorded ground motions of the earthquake is provided by Baltay and Boatright (2015). The moniker “odd couple” is appropriate for the pair of bridges across the Carquinez Strait, because each bridge is of a different design and a different age. The westbound suspension bridge (CGS station 68185), also known as the Alfred Zampa Memorial bridge, opened for service in 2003, when it replaced an older 1927‐era‐construction cantilever truss bridge that was deemed seismically unsafe. The eastbound cantilever truss bridge (CGS station 68184) opened for service in 1958. Figure 1 shows the layout of the two bridges and the locations of the associated geotechnical arrays. The inset in the figure indicates where the bridges are with respect to San Francisco, California. A photograph of both bridges is provided in Figure 2. The azimuths of the west‐ and east‐bound bridges are listed as 358° and 357°, respectively (Center of Engineering Stron Motion Data [CESMD] at http://www.strongmotioncenter.org/NCESMD/photos/CGS/lllayouts/ll68185.pdf and http://www.strongmotioncenter.org/NCESMD/photos/CGS/lllayouts/ll68184.pdf; last accessed April 2015). These parallel bridges are important lifelines on Interstate 80, connecting the California cities of Crockett and Vallejo, the San Francisco Bay area and the Sacramento regions, and the well‐known Napa Valley wine‐country and much of the remainder of northern …

Health monitoring of an instrumented SRMF building using earthquake data

SUMMARYThis paper is a study of a six‐story welded steel moment‐resisting frame instrumented by California Strong Motion Instrumentation Program. Several earthquakes had shaken the building, and its response of strong motion data recorded during the earthquakes were made available. In particular, the Whittier Narrows (October 1987), Sierra Madre (June 1991), Northridge (January 1994) and Chino Hills (July 2008) earthquakes were considered in the studies reported here.The paper investigates the capability of input–output system identification methods, namely eigensystem realization algorithm with data correlation, and observer Kalman filter identification, in identifying dynamic characteristics of typical office building structures subjected to strong ground motion. It explores the possibility to extend the above system identification procedures to near‐real‐time estimation of the building response under future earthquakes in order to estimate the likelihood of brittle damage in welded beam to column connections. The modal identification results are compared with those obtained using the spectral analysis and the deterministic‐stochastic subspace identification method to verify the accuracy of the identified modal parameters. Copyright © 2013 John Wiley & Sons, Ltd.

Evaluation of current seismic design equations for nonstructural components in tall buildings using strong motion records

SUMMARYA recently completed California Strong Motion Instrumentation Program (CSMIP) data interpretation project used recorded ground and floor motion data to evaluate a key ASCE/SEI 7‐05 (and 7‐10) equation for seismic design of acceleration‐sensitive building nonstructural components. CSMIP motions from 73 earthquakes recorded in 151 fixed‐base buildings were used in the evaluation. An improved equation was developed with two categories of revisions. First, the current code formula considers a linear relationship between the peak floor acceleration (PFA) and the relative height of the component in the building with a roof PFA that is three times that of the peak ground acceleration. The analyses of the recorded motions showed that improved results could be obtained by using a nonlinear relationship and by considering both the building approximate period, Ta, and the level of ground motion. Second, the code formula considers a component amplification factor, ap, that takes values between 1.0 and 2.5 depending on the flexibility of the nonstructural component. Analyses showed that component amplification factor can be better represented using a three‐segment spectrum composed of a linear rise from 1.0 to maximum value of ap at short periods, a flat segment with the maximum value of ap at medium‐range periods and a nonlinear decaying segment at longer periods. The shape and amplitude of the spectrum were found to vary depending on Ta. This paper evaluates tall buildings with at least 15 stories using the proposed equations and confirms that the revisions provide improvements in matching design equations with recorded response. Copyright © 2011 John Wiley & Sons, Ltd.

Seismic Response Characteristics of Deep Soft Site with Depth under Far-Field Ground Motion of Great Earthquake

Considering the dynamic nonlinear characteristics of soil by equivalent linear method, one-dimensional wave models were established to study the seismic effects along depth of deep soft sites under far-field ground motions of great earthquake. The results show that the magnified effect of acceleration response spectrum of each layer present more outstanding under far-field ground motions than under Suzhou artificial waves, with the increasing of bedrock peak ground acceleration, there is probability that the peak of long-period component of acceleration response spectrum appears higher than that of the short-period within 15m depth, which may adversely affect the long-period building structures. However, the reduction coefficient of peak ground acceleration (PGA) along depth according to the three levels of earthquake fortification standard was relatively higher when inputting far-field ground motions of great earthquake. As the curve fitted by Longjun Xu et al. based on records collected California Strong Motion Instrumentation Program geotechnical arrays of the United States and Hosokura Mine arrays of Japan, is not suitable for Suzhou area, suited quantitative formula about reduction coefficient curve of PGA with depth in deep soft site is given. Besides, maximum shear strain at the depth of approximately 15m and 40m present to be greatly changed when inputting far-field ground motions of great earthquake, with the growth of inputting bedrock peak ground acceleration, the layer in the depth of about 15m comes to be the most unfavorable position of shear deformation.

IDENTIFICATION OF DYNAMIC PARAMETERS OF STRUCTURES USING EARTHQUAKE DATA

The seismic performance of steel moment-framed buildings has been of particular interest after the 1994 Northridge earthquake because brittle fractures were discovered at the beam-column connection. This paper examines the problem of identifying the dynamic character stics of an instrumented building using an input-output system identification method. The building studied was a six-story steel moment-resisting frame (SMRF) instrumented by the California Strong Motion Instrumentation Program (CSMIP). The building was shaken by several earthquakes and strong motion data of the building response was recorded during these earthquakes and were made available through SMIP. The identified modal properties of the structure were compared and verified with the spectral analysis of the response of the structure excited by three different earthquakes.

Variation of earthquake ground motion with depth

The variation of ground motion with depth is investigated in this paper, which is essential in determining the seismic design ground motion for embedded structures and pipelines. Firstly the earthquake ground motion on surface and in subsoil recorded by Hosokura Mine array of Japan and six California Strong Motion Instrumentation Program geotechnical arrays of the United States from about fifty moderate and strong earthquakes are described. Then the arrays were classified into three different categories according to their site conditions. Finally the variation law of ground and sub-ground motion with depth is established as a result of a nonlinear regression analysis of the above-mentioned data. Through comparing the features in different sites, it is concluded that, in general, the amplitude (acceleration, velocity and displacement) of ground motion are decreasing with depth and the attenuation rate is higher in the shallow strata than that in deeper ones.

TriNet Strong-Motion Data from the M 7.1 Hector Mine, California, Earthquake of 16 October 1999

The M_w 7.1 Hector Mine earthquake of October 16, 1999 was recorded by more than 300 stations of TriNet, which is administered cooperatively by the California Division of Mines and Geology's California Strong Motion Instrumentation Program (CDMG/CSMIP), California Institute of Technology, and the U.S. Geological Survey (USGS). The earthquake occurred in a remote part of the Mojave Desert, approximately 190 km northeast of downtown Los Angeles, and there were no strong-motion stations close to the surface rupture. The nearest station, Hector, is about 27 km north of the epicenter; it recorded a peak horizontal ground acceleration of 0.33g. The two next closest stations, Amboy and Joshua Tree, are to the east and south, both at epicentral distances of about 50 km; each recorded peak ground accelerations of about 0.2g. The new digital instruments installed for the TriNet project recorded a large set of reliable data at epicentral distances up to 275 km. These data can significantly improve empirical peak ground motion attenuation relationships, which are usually developed for distances only up to 100 km (Boore et al., 1993, 1997) because adequate data have not been available at greater distances. Hector Mine peak ground motions demonstrate reasonable agreement with empirical attenuation relationships for acceleration. In contrast, higher than expected ground velocities and displacements were recorded at epicentral distances of about 150 to 220 km, especially in the Los Angeles sedimentary basin, where anomalously high-amplitude displacements with periods of 6 to 7 sec were recorded in Los Angeles, Long Beach, and other areas. These long-period surface- or basin-generated waves can have significant effects on large structures. The M_w 7.3 Landers earthquake of 1992 similarly produced strong, long-period waves in the basin. The peak ground motions produced by the Landers earthquake were on average 1.6 times higher than for the Hector Mine earthquake in the Los Angeles area. Ground-motion data recorded by digital instruments were uniformly processed in the frequency band 0.067 to 46 Hz (0.022–15 sec). The processed data set includes records from 213 ground-response stations. In an effort to make strong-motion data available quickly to the engineering and scientific communities, important records from this event were made available by file transfer protocol (ftp) beginning the day of the earthquake.

Base-Isolated FCC Building: Impact Response in Northridge Earthquake

The base-isolated Fire Command and Control (FCC) building in Los Angeles experienced strong motion during the 1994 Northridge earthquake. The California Strong Motion Instrumentation Program has instrumented the building and recorded the data during the Northridge earthquake; these data are available for performance evaluation. Impact was observed in the base-isolated FCC building during the Northridge earthquake. The objective of this study is to evaluate the seismic performance of the base-isolated FCC building during the 1994 Northridge earthquake and the effect of impact. New analytical modeling techniques are developed to analyze the base-isolated FCC building with impact and are verified using system identification. The response computed, using the developed analytical modeling techniques, is verified using recorded data. The response with and without impact is presented. The effects of impact on the structural response are evaluated. The seismic performance evaluations, comparing the response of the base-isolated building with the response if the building were fixed base, are presented. It is shown that the seismic performance of the FCC building in the Northridge earthquake was satisfactory, except for increased shear and drift due to impact. Impact should be avoided in base-isolated structures as it can cause damage.

The SCEC Phase III Strong-Motion Database

As part of the Southern California Earthquake Center (SCEC) Phase III effort to include site effects in hazard models for southern California, a regional database of strong-motion observations was developed. The observations consist of the peak ground acceleration (PGA) and 5% damped response spectral acceleration (SA) at 0.3-, 1.0-, and 3.0-sec periods from 28 earthquakes and 281 stations. A total of 449 pairs of horizontal PGA and SA observations that were taken from the SCEC Strong-Motion Database (SMDB) are presented here. The phase III database includes earthquakes with moment magnitudes larger than 5.0 and stations in southern California with locations between 32° and 36° north latitude. Observations from buildings with more than two stories and dam abutments or crests are excluded from the database. Observations with distances of 150 km or greater were also excluded. The agencies that provided the data to SMDB are the U.S. Geological Survey, California Strong Motion Instrumentation Program, University of Southern California, and the Los Angeles Department of Water and Power. The database also contains site classification information for each station. A first general classification is based on the 1:750,000 California map of Quaternary, Tertiary, and Mesozoic geologic units by Jennings (1977) as modified by Park and Elrick (1998). A second more detailed classification is based on Quaternary mapping in the Los Angeles region by Tinsley and Fumal (1985) as modified by Park and Elrick (1998). A third classification is based on the correlation of surface geology with shear-wave velocity in the upper 30 m (Wills et al., 2000). An arbitrary “depth-to-basement” parameter is assigned to stations that are located within the boundary of the 3D velocity model used by Olsen (2000), which is based on the SCEC 3D velocity model (version 1). This parameter is defined as the depth to the 2.5km/sec velocity isosurface. Special parameters associated with particular attenuation relations, such as different distance measures, a hanging wall flag, and fault-type flag are also assigned to each observation. These data are all presented within the tables and figures of this article, and also have been made available via a downloadable file on the Internet ( http://smdb.crustal.ucsb.edu/~phase3 ).

Response of Base-Isolated USC Hospital Building in Northridge Earthquake

The base-isolated University of Southern California (USC) hospital building experienced strong motion during the 1994 Northridge earthquake. California Strong Motion Instrumentation Program data of the response are available for performance evaluation. The objective of this study is to evaluate the seismic performance of the base-isolated USC hospital building during the 1994 Northridge earthquake. A nonlinear analytical model of the USC hospital building is developed and verified using system identification. The response computed, using the presented analytical modeling techniques, is verified using recorded data. Structural behavior during the Northridge earthquake is evaluated in detail. The base-isolated USC hospital building performed well and reduced the response when compared to a fixed-base structure. The free-field acceleration was 0.49g and peak foundation/ground acceleration was 0.37g. The peak roof acceleration was reduced to 0.21g, nearly 50% of the peak ground acceleration. The peak drift wa...

Soil-Foundation-Structure Behavior at the Oakland Outer Harbor Wharf

The California Strong Motion Instrumentation Program's Loma Prieta records at Oakland Outer Harbor Wharf maybe used to study the free-field motions, the possible softening of soils surrounding the piles supporting the instrumented wharf, the determination of the motion on the instrumented wharf using free-field motion input and deflection-compatible lateral and vertical pile foundation stiffnesses, and conditions under which a soil-foundation interaction failure or structural failure of the batter piles might have developed.