National Strong Motion Network Research Articles

Seismological and engineering characteristics of strong motion data from 24 and 26 September 2019 Marmara Sea earthquakes

An MW 4.5 earthquake took place on September 24, 2019 in the Marmara Sea. Two days after, on September 26, 2019, Marmara region was rattled by an MW5.7 earthquake. With the intention of compiling an ample strong ground motion data set of recordings, we have utilized the stations of Istanbul Earthquake Rapid Response and Early Warning System operated by the Department of Earthquake Engineering of Boğaziçi University and of the National Strong Motion Network operated by AFAD. Altogether 438 individual records are used to calculate the source parameters of events; namely, corner frequency, radius, rupture area, average source dislocation, source duration and stress drop. Some of these parameters are compared with empirical relationships and discussed extensively. Duration characteristics are analysed in two steps; first, by making use of the time difference between P-wave and S-wave onsets and then, by considering S-wave durations and significant durations. It is observed that they yield similar trends with global models. PGA, PGV and SA values are compared with three commonly used ground motion prediction models. At distances closer than about 60 km, observed intensity measures mostly conform with the GMPE predictions. Beyond 60 km, their attenuation is clearly faster than those of GMPEs. A frequency-dependent Q model is developed by using both events. Its consistency with existing regional models is confirmed.

Ground-motion model for subduction earthquakes in northern South America

Subduction ground motions in northern South America are about a factor of 2 smaller than the ground motions for similar events in other regions. Nevertheless, historical and recent large-interface and intermediate-depth slab earthquakes of moment magnitudes Mw = 7.8 (Ecuador, 2016) and 7.2 (Colombia, 2012) evidenced the vast potential damage that vulnerable populations close to earthquake epicenters could experience. This article proposes a new empirical ground-motion prediction model for subduction events in northern South America, a regionalization of the global AG2020 ground-motion prediction equations. An updated ground-motion database curated by the Colombian Geological Survey is employed. It comprises recordings from earthquakes associated with the subduction of the Nazca plate gathered by the National Strong Motion Network in Colombia and by the Institute of Geophysics at Escuela Politécnica Nacional in Ecuador. The regional terms of our model are estimated with 539 records from 60 subduction events in Colombia and Ecuador with epicenters in the range of −0.6° to 7.6°N and 75.5° to 79.6°W, with Mw≥4.5, hypocentral depth range of 4 ≤ Zhypo ≤ 210 km, for distances up to 350 km. The model includes forearc and backarc terms to account for larger attenuation at backarc sites for slab events and site categorization based on natural period. The proposed model corrects the median AG2020 global model to better account for the larger attenuation of local ground motions and includes a partially non-ergodic variance model.

Processing Data from Vibration Recordings

The article aims to present a way of processing the data within a real-time transmission system of recorded vibration. At present, Romanian National Strong Motion Network for Constructions of URBAN-INCERC has 56 seismic / digital accelerometer stations, of which 46 are in territory and 10 in Bucharest. The seismic stations of this system are placed in some ground floor-buildings type, assimilated with the free-field, or in buildings with 1-3 levels. First application of the real-time transmission system is related to the accelerometric records from moderate earthquakes, which have shown a spatial distribution of PGA with NE-SW directivity, similar to that observed under certain conditions of seismic severity in previous strong earthquakes. Some charts illustrating the acceleration amplitudes recorded from the 2016 and 2017 earthquakes in the URBAN-INCERC network will be shown. The second application is referred to the structural response (structural behaviour under ambient vibrations or moderate and severe seismic motions). Generally, the spectral analysis of these records leads to getting: the natural frequencies, the influence of the general directivity of waves propagation specific to the Vrancea source (on the spectral content and on structural response), the influence of the local soil conditions etc. In this case, for a study building, the vibration modes, the drift/the relative floor displacement etc. can result from this processing, with a validation based on a structural modelling with finite elements. The seismic wave propagation direction is the first option for determining the direction of propagation of severe effects on buildings. The correlation between them can be validated by the existence of pre-event dynamic characteristics of those buildings (before a major seismic event) and at post-event time.

Natural Disasters and Demand for Redistribution: Lessons from an Earthquake

The literature shows that when a society believes that wealth is determined by random “luck” rather than by merit, it demands more redistribution. Adverse shocks, like earthquakes, strengthen the belief that random “bad luck” can frustrate the outcomes achieved with merit. We theoretically illustrate that individuals react to such shocks by raising support for redistribution. We then present evidence of this behavior by exploiting a natural experiment provided by one of the strongest seismic events that occurred in Italy in the last three decades, the L’Aquila earthquake in 2009. We assemble a novel dataset by matching information on the ground acceleration registered throughout the National Strong Motion Network during the earthquake with survey data about individual opinions on redistribution collected a few months later. The empirical analysis illustrates that the intensity of the shakes is associated with subsequent stronger beliefs that, for a society to be fair, income inequalities should be levelled by redistribution.

Empirical Attenuation relationship for Peak Ground Horizontal Acceleration for North-East Himalaya

Empirical Attenuation relationship for Peak Ground Horizontal Acceleration for North-East Himalaya

Characteristics of strong ground motions in the 2014 Ms 6.5 Ludian earthquake, Yunnan, China.

The 2014 M s 6.5 (M w6.1) Ludian earthquake occurred in the eastern Sichuan–Yunnan border region of western China. This earthquake caused much more severe engineering damage than the usual earthquakes with the same magnitude in China. The National Strong Motion Network obtained large set of ground motion recordings during the earthquake. To investigate the engineering interested characteristics of ground motion from Ludian earthquake and compare it with the M w 7.9 Wenchuan and the M w 6.6 Lushan earthquakes in western China, studies on the ground motion field, attenuation relationship, distance dependence of significant duration, and site amplification were carried out. Some conclusion is drawn. Specifically, the ground motion field reveals a directional feature, and the distribution characteristics of the two horizontal components are similar. The attenuation relationship for Ludian earthquake is basically consistent with the ground motion prediction equation (GMPE) for western China, except the slight smaller than the GMPE predicted at short periods. The distance dependences of ground motion duration are different in Sichuan and Yunnan regions due to the local physical dispersion and Q value. The site amplification factors are dominated by linear site response for lower reference ground motion, but the nonlinearity becomes notable for higher reference ground motion. This feature is basically consistent with the empirical model for western China. All the results indicate that the spatial distribution of ground motion, the attenuation characteristics, and the site amplification effect should be considered in characterization of near-field ground motion.

ISMD, a Web Portal for Real-Time Processing and Dissemination of INGV Strong-Motion Data

Online Material: Earthquake catalog and strong motion stations. In Italy, strong‐motion monitoring started in the early 1970s, when the Rete Accelerometrica Nazionale (RAN, the Italian National Strong Motion Network; http://www.protezionecivile.gov.it/jcms/it/ran.wp; see Data and Resources for a complete listing of all websites listed in this article) was designed and installed by the Agenzia Nazionale per le Nuove Tecnologie, l’Energia e lo Sviluppo Economico Sostenibile (ENEA) and ENEL (an Italian power company). The aim was to evaluate the seismic risk in connection with the construction of nuclear power plants. Since 1997, the RAN (Gorini et al. , 2010) has been run by the Dipartimento della Protezione Civile (DPC). At present, the RAN includes about 500 digital strong‐motion stations. The contribution of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) to Italian strong‐motion monitoring started some years later. Through the 2004–2006 agreement between the INGV and the DPC (Strong‐Motion Stations Project), the INGV began the phase of strong‐motion monitoring (Augliera et al. , 2010, 2011). Since 2006, a complete renewal of the (velocimetric) Rete Sismica Nazionale (RSN; Amato and Mele, 2008) was made by installing accelerometers to sites where broadband RSN velocimeters were already present. Altogether, the current ∼150 high‐dynamics digital strong‐motion stations that cover the Italian territory constitute the INGV strong‐motion network. The first channel chosen by the INGV to disseminate the recorded waveforms was through the European Integrated Data Archive (EIDA; http://eida.rm.ingv.it/; http://www.orfeus-eu.org/eida/eida.html), a web portal devoted to seismic data exchange that was developed in the framework of the Network of Research Infrastructures for European Seismology (NERIES) European project (www.neries-eu.org, Networking Activity 3 [NA3]). Since 2008, the INGV raw signals have been downloadable in the Standard for the Exchange of Earthquake Data (SEED) format from the continuous data archive of the INGV National Earthquake Centre (Centro Nazionale Terremoti, CNT). …

Evaluation of the national strong motion network in Greece: deployment, data-processing and site characterization

In this paper a brief introduction regarding the latest advancements of strong motion instrumentation programs in Greece since the first accelerograph was installed by NOA-IG is given. Analytical description of various utilized analog and digital accelerographic sensors is presented and the evolution of the different types of data processing techniques applied by the two research centers is given using recordings from both Institutes. The site characterization of the strong motion recording sites and the available information for those stations are presented as well. A final evaluation and correlation of the previous proposed configuration of the Hellenic accelerographic networks ITSAK and NOA-IG resulted from previous study (Theodoulidis et al. in Planning of strong motion network. pp 86–04, 1986) in regard to the new strong-motion installations within the framework of EPPO’s project is accomplished.

A κ Model for Mainland France

An important parameter for the characterization of strong ground motion at high-frequencies (>1 Hz) is kappa, κ, which models a linear decay of the acceleration spectrum, a(f), in log-linear space (i.e. a(f) = A 0 exp(− π κ f) for f > f E where f is frequency, f E is a low frequency limit and A 0 controls the amplitude of the spectrum). κ is a key input parameter in the stochastic method for the simulation of strong ground motion, which is particularly useful for areas with insufficient strong-motion data to enable the derivation of robust empirical ground motion prediction equations, such as mainland France. Numerous studies using strong-motion data from western North America (WNA) (an active tectonic region where surface rock is predominantly soft) and eastern North America (ENA) (a stable continental region where surface rock is predominantly very hard) have demonstrated that κ varies with region and surface geology, with WNA rock sites having a κ of about 0.04 s and ENA rock sites having a κ of about 0.006 s. Lower κs are one reason why high-frequency strong ground motions in stable regions are generally higher than in active regions for the same magnitude and distance. Few, if any, estimates of κs for French sites have been published. Therefore, the purpose of this study is to estimate κ using data recorded by the French national strong-motion network (RAP) for various sites in different regions of mainland France. For each record, a value of κ is estimated by following the procedure developed by Anderson and Hough (Bull Seismol Soc Am 74:1969–1993, 1984): this method is based on the analysis of the S-wave spectrum, which has to be performed manually, thus leading to some uncertainties. For the three French regions where most records are available (the Pyrenees, the Alps and the Cotes-d'Azur), a regional κ model is developed using weighted regression on the local geology (soil or rock) and source-to-site distance. It is found that the studied regions have a mean κ between the values found for WNA and ENA. For example, for the Alps region a κ value of 0.0254 s is found for rock sites, an estimate reasonably consistent with previous studies.

The recently compiled Turkish strong motion database: preliminary investigation for seismological parameters

Strong motion data recorded by the Turkish national strong motion network has been compiled and processed systematically for the first time, together with detailed geophysical and geotechnical site measurements for all of its stations. The catalog information of 18 seismological agencies and other sources were examined to obtain reliable source, geometry, and distance parameters for each event. The high quality digital and analog strong motion data was processed by a uniform methodology to remove the high- and low-frequency noise. Currently, the seismological and spectral information of 4,607 strong motion records are available for use by earth scientists and earthquake engineers. In this article, we present the fundamental features of this database and explain our methodology in their calculation. We present several comparisons of our database with other related studies to verify our approach during the computational stage of the seismological parameters. The results confirm the reliability of our calculations. The database has also enabled us to derive empirical magnitude conversion relationships to estimate moment magnitude in terms of different magnitude scales. The article ends with a discussion of the likely improvements in the European accelerometric data through contributions from this strong motion database applicable for seismically active shallow-crust regions. The findings of this article emphasize the necessity of global strong motion databases in Europe for better estimation of seismic hazard in regions of similar seismotectonic environment.

ML and MW Scales in the Iranian Plateau Based on the Strong-Motion Records

The availability of a large amount of strong-motion data recorded by the National Strong Motion Network of Iran (nsmni) has motivated this study to develop relations for routine determination of M L and M W from digital horizontal components of the strong-motion records. The dataset comprises 861 two-component horizontal acceleration time series recorded for 125 earthquakes with magnitudes of 4.5 and larger. The M L scale is based on the horizontal synthesized Wood–Anderson seismograms. We have applied the Monte Carlo technique to evaluate distance correction curves for use in determining the local magnitude, M L , in Iran and in its northern, eastern, and Zagros subregions. Results indicate that the distance correction curves show trilinear behavior for geometrical spreading. The resulting coefficients evaluated for Iran as a whole are: R 1 = 96 ± 5 km; R 2 = 131 ± 5 km; n 1 = 1.01 ± 0.02; n 2 = −0.14 ± 0.1; n 3 = 0.14 ± 0.03; k = 0.00020 ± 0.00008. The distances less than R 1 correspond to attenuation of the direct waves. Between R 1 and R 2 is the distance where the multiply reflected and refracted shear waves from Moho dominate the arrivals. n 1 , n 2 , and n 3 are the coefficients of geometrical spreading for distances from the source to R 1 , R 1 to R 2 , and beyond R 2 . k is the coefficient of inelastic attenuation. For estimating the M W scale from the strong-motion data, we used the method proposed by Andrews (1986). To find the best correlation between the moment magnitudes measured from the strong-motion data and those measured from teleseismic data, we examined several time windows (e.g., whole trace, S -wave coda, and source time durations). The regressions show that the M W estimates from different time windows are all equally well correlated with the corresponding reported values with nearly identical standard deviations. Finally, relations between the estimates of local and moment magnitudes for the regions show that for earthquakes with magnitudes larger than about 6.0, the M L scale gradually becomes saturated and, therefore, it gives smaller values than those obtained by the M W scale. However, for smaller earthquakes, the M L scale overestimates the M W scale. This discrepancy occurs mainly because the frequency contents of the waveforms employed in these scales are different.

Enhancement of the National Strong-Motion Network in Turkey

Two arrays comprising 20 strong-motion sensors were established in western Turkey. The 14 stations of BYTNet follow a N-S trending line about 65 km in length, normal to strands of the North Anatolian fault that runs between the cities of Bursa and Yalova. Here the dominant character of the potential fault movement is a right-lateral transform slip. The DATNet array, comprising a total of eight stations, is arranged along a 110-km-long E-W trending direction along the Menderes River valley between Denizli and Aydin. (Two stations in this array were incorporated from the existing Turkish national strong-motion network.) This is an extensional tectonic environment, and the network monitors potential large normal-faulting earthquakes on the faults in the valley. The installation of the arrays was supported by the North Atlantic Treaty Organization (NATO) under its Science for Peace Program. Maintenance and calibration is performed by the General Directorate of Disaster Affairs (GDDA) according to a protocol between Middle East Technical University (METU) and GDDA. Many young engineers and scientists have been trained in network operation and evaluation during the course of the project, and an international workshop dealing with strong-motion instrumentation has been organized as part of the project activities.

A Critical Examination of Near-Field Accelerograms from the Sea of Marmara Region Earthquakes

In 1999, Turkey was struck by two major earthquakes that occurred 86 days apart on the North Anatolian Fault system. Both earthquakes had right-lateral strike-slip mechanisms with moment magnitudes greater than 7. The number of strong-motion records obtained from the Kocaeli earthquake (17 August 1999, M w 7.4) was 34. The second event, designated as the Bolu-Duzce earthquake (12 November 1999, M w 7.2), triggered 20 instruments. Among the records that we have from these earthquakes, seven are from near-source ground-motion data. These records were obtained from the cities of Gebze (GBZ), Yarimca (YPT), Izmit (IZT) (capital city of the province of Kocaeli), Adapazari (SKR) (capital of the province of Sakarya), Duzce (DZC) (shaken strongly in both the events), and Bolu (BOL). In many of these urban centers, extensive structural damage was observed. Although these near-field data have greatly expanded the strike-slip near-source ground-motion database worldwide for M w >7 earthquakes, they represent a blurred image of the actual severity of the ground motions in the epicentral area because of the sparseness of the national strong-motion network and the unrepresentative geologic conditions at the recording sites. We examine the records to determine whether they provide clues about the extensive damage on the housing stock in the epicentral region. The goal is tackled with earthquake structural engineering criteria in mind, using the drift spectrum as the primary yardstick. There appears to be conflicting evidence that the fault-normal (FN) direction should represent a greater damage-causing potential when this potential is based on ground-story drift spectra. The component with larger ground velocity does correlate better with the component with larger drift demand, but this does not always coincide with the FN direction. The period of the peak velocity pulse matches the structural period where the drift demand is the largest. Further refinements of code requirements that consider this effect are in order. Manuscript received 20 August 2000.

Spanish national strong motion network. Recording of the Huelva earthquake of 20 December, 1989

In recent years a network of 30 accelerographs has been installed through the zones of highest seismic activity of Spain. For the first time, digital strong motion records have been obtained in Spain, with a maximum horizontal acceleration value of 0.06 g. A comprehensive study is made of the strong motion recordings of an earthquake which occurred in southwest Spain, on December 20, 1989. The isoseismal map is drawn and the data confirm the main attenuation directions in the area observed in other shocks.