National Strong Motion Observation Network System Research Articles

Earthquake Source database for Chinese strong motion flatfile in 2007-2020

The National Strong-Motion Observation Network System of China has collected over 12000 strong-motion recordings from 2007 to December 2020. This study compiled the source-related metadata of totally 1920 earthquakes associated with assembled well-processed recordings of China. The earthquake basic information, focal mechanisms, and the fault geometry were collected from various institutes and literature. We recommended the MW values for 900 earthquakes, the fault types for 1064 earthquakes, and the fault geometries for 18 large earthquakes. We also performed the statistics analysis for establishing the empirical conversions of MW-MS, and ML, and providing the empirical relationships between MW and ruptured area, aspect ratio, respectively. Moreover, the ruptured fault geometries of large earthquakes were used to preliminarily divide all earthquakes considered into 1141 mainshocks, and 779 aftershocks. The finite-fault distances (RJB and Rrup) of strong-motion recordings from the 18 large earthquakes were calculated, and then used to yield the statistic relationships between the point-source distances (Repi and Rhyp) and finite-fault distances. We finally provided the earthquake source database freely accessible at website. The source-related metadata can be directly applied to develop the ground motion prediction equations of China.

Site database for national strong motion stations in mainland China

Ground motion amplification and spectral content are significantly influenced by local soil and geological conditions. This article summarizes the development of the China Site Database (CNSDB) in the China Ground Motion Flatfile project. CNSDB contains site information for 1450 strong-motion recording stations within the National Strong Motion Observation Network System (NSMONS) in China. The primary site information in CNSDB includes the time-averaged shear-wave velocity in the upper 30 m (VS30), and site class according to the seismic design code in China. These site data are derived using different methods from various data sources. Priority is given to approaches that minimize bias and dispersion relative to measurement-based results. Recommended VS30 values and site class are derived from reliable velocity profiles or field survey results whenever available. A China-specific VS30 extrapolation model is developed using 6179 engineering boreholes and is then utilized to estimate VS30 for profiles <30 m. VS30 values and site class are estimated from horizontal-to-vertical spectral ratio (HVSR) curves of earthquake recordings using machine-learning techniques. For the remaining sites without velocity profiles or sufficient ground-motion recordings for HVSR computation, VS30 values are determined as the weighted average of proxy-based estimates using geological attributes, topographic slope, and terrain categories. We also discuss the potential application of CNSDB in the development of China seismic hazard map considering site amplification factors.

Soil Profile Database and Site Classification for National Strong-Motion Stations in Western China

Abstract As part of a broader effort to develop ground-motion data resources for China in a manner consistent with Next Generation Attenuation projects, we develop a database of geotechnical soil profiles and shear-wave velocity (VS) logs for sites having ground-motion accelerometers (this database is referred to as soil profile database [SPD]), and then use that data to develop site parameters. The site information is compiled for stations within the National Strong Motion Observation Network System (NSMONS) of China. This effort is focused on four provinces in western China (Yunnan, Sichuan, Gansu, and Xinjiang), which contribute 871 of 2023 NSMONS stations throughout China. Of the 871 sites, the SPD provides site information for 678 sites, or 78% of the total. To develop the SPD, geotechnical logs and/or VS profiles are compiled for 637 sites. This information is derived from previously unpublished reports and is assembled here in a uniform format and partially disseminated (only approximate site locations are provided). The remaining 41 sites in the SPD have confirmed bedrock conditions at the ground surface. Site metadata and parameters are compiled into a database, included as a supplemental material to this article, that includes the depth to the first occurrence of 0.5 km/s shear-wave velocity (Z0.5), three time-averaged shear-wave velocity parameters (VSe, VS20, VS30), and site classifications based on the Chinese building seismic design code and National Earthquake Hazards Reduction Program Provisions. For sites with VS profiles that do not extend to 30 m, we present region-specific recommendations for extrapolating time-averaged velocities from the profile depth to 30 m. For sites with geotechnical logs but no profiles, we present procedures to estimate VS profiles from which the earlier parameters can be derived.

Empirical Correlations between Generalized Ground-Motion Intensity Measures for Earthquakes in China

ABSTRACTThis study used earthquake records from China to investigate comprehensively the correlation coefficients between various intensity measures (IMs), including peak ground acceleration, peak ground velocity, spectral acceleration, spectrum intensity, acceleration spectrum intensity, Arias intensity, cumulative absolute velocity, and significant duration. After collection of metadata information, 681 three-component ground-motion recordings with magnitudes of Mw 4.9–6.9 were carefully processed and extracted from the China National Strong-Motion Observation Network System dataset (2007–2015). The applicability of both the Next Generation Attenuation (NGA)-West2 ground-motion model (GMM) and of other GMMs was verified for different IMs, regarding the China dataset. Then, empirical correlation coefficients between different IMs were computed, considering the uncertainty due to the different sample sizes of the observational data using the bootstrap sampling method and Fisher z transformation. Finally, the median values of the correlation coefficients were fitted as a continuous function of the vibration period in the range of 0.01–10.0 s and compared with the results of similar studies developed for shallow crustal regions worldwide. The developed region-specific correlation coefficient prediction model yielded tendencies approximately like those reported in other studies. However, obvious differences were found in long-period ranges of amplitude-based IMs, cumulative effect IMs, and significant duration. These results suggest the necessity of using region-specific correlation coefficients for generalized IMs in China. The presented results and parametric models could be easily implemented in a generalized IM ground-motion selection method or a vector-based probability seismic hazard analysis procedure for China.

Site classification for National Strong Motion Observation Network System (NSMONS) stations in China using an empirical H/V spectral ratio method

Reliable site classification of the stations of the China National Strong Motion Observation Network System (NSMONS) has not yet been assigned because of lacking borehole data. This study used an empirical horizontal-to-vertical (H/V) spectral ratio (hereafter, HVSR) site classification method to overcome this problem. First, according to their borehole data, stations selected from KiK-net in Japan were individually assigned a site class (CL-I, CL-II, or CL-III), which is defined in the Chinese seismic code. Then, the mean HVSR curve for each site class was computed using strong motion recordings captured during the period 1996–2012. These curves were compared with those proposed by Zhao et al. (2006a) for four types of site classes (SC-I, SC-II, SC-III, and SC-IV) defined in the Japanese seismic code (JRA, 1980). It was found that an approximate range of the predominant period Tg could be identified by the predominant peak of the HVSR curve for the CL-I and SC-I sites, CL-II and SC-II sites, and CL-III and SC-III+SC-IV sites. Second, an empirical site classification method was proposed based on comprehensive consideration of peak period, amplitude, and shape of the HVSR curve. The selected stations from KiK-net were classified using the proposed method. The results showed that the success rates of the proposed method in identifying CL-I, CL-II, and CL-III sites were 63%, 64%, and 58% respectively. Finally, the HVSRs of 178 NSMONS stations were computed based on recordings from 2007 to 2015 and the sites classified using the proposed method. The mean HVSR curves were re-calculated for three site classes and compared with those from KiK-net data. It was found that both the peak period and the amplitude were similar for the mean HVSR curves derived from NSMONS classification results and KiK-net borehole data, implying the effectiveness of the proposed method in identifying different site classes. The classification results have good agreement with site classes based on borehole data of 81 stations in China, which indicates that our site classification results are acceptable and that the proposed method is practicable.

Rupture Directivity from Strong-Motion Recordings of the 2013 Lushan Aftershocks

Abstract The observed directivity effects of ground motion have extensive implications for both earthquake source physics and earthquake-hazard analyses on active fault zones. In general, it is still difficult to determine the rupture directivity in detail for smaller earthquakes because of limited azimuthal coverage. Four Lushan aftershocks that occurred on 20 and 21 April 2013 (events I, II, III, and IV) were well recorded by the National Strong-Motion Observation Network System of China. An interesting phenomenon was clearly observed: the distributions of the triggered stations for the four aftershocks, which had adjacent hypocenters and similar magnitudes, differed significantly from each other. The analyses of ground-motion parameters, including the peak ground-motion parameters, response spectra, and durations, indicate that the directivity of the ground motion was significant for events II and III. The Fourier spectral ratio method was used to imprint the rupture directivity. We calculated the rupture direction and rupture velocity by inverting the peak parameters. Random realizations in many times were utilized to consider the uncertainty in the results of the inversion. The results indicate that the four events shared the similar northeast–southwest-trending fault plane and had similar rupture velocities of approximately 2.1km/s. Event I was more likely to be a perfectly symmetric bilateral rupture, though there was large uncertainty in the results of the inversion. The rupture for events II and III propagated predominantly toward the southwest. However, event IV was observed to have an approximately symmetric bilateral propagation, slightly inclining to the northeast. We also confirmed the period-dependent directivity effect by inverting the response spectra at different periods.

Characteristics of strong motions and damage implications of M S6.5 Ludian earthquake on August 3, 2014

The Ludian County of Yunnan Province in southwestern China was struck by an M S6.5 earthquake on August 3, 2014, which was another destructive event following the M S8.0 Wenchuan earthquake in 2008, M S7.1 Yushu earthquake in 2010, and M S7.0 Lushan earthquake in 2013. National Strong-Motion Observation Network System of China collected 74 strong motion recordings, which the maximum peak ground acceleration recorded by the 053LLT station in Longtoushan Town was 949 cm/s2 in E–W component. The observed PGAs and spectral ordinates were compared with ground-motion prediction equation in China and the NGA-West2 developed by Pacific Earthquake Engineering Researcher Center. This earthquake is considered as the first case for testing applicability of NGA-West2 in China. Results indicate that the observed PGAs and the 5 % damped pseudo-response spectral accelerations are significantly lower than the predicted ones. The field survey around some typical strong motion stations verified that the earthquake damage was consistent with the official isoseismal by China Earthquake Administration.

Strong-Motion Observations of the Lushan Earthquake on 20 April 2013

Online Material: Additional figures of acceleration time series; table of station parameters, associated ground motion intensities. On 20 April 2013, at 08:02 a.m. Beijing time, a strong earthquake hit Lushan, a county in the southwest of Sichuan Province in China. During this earthquake, a total of 114 strong‐motion stations from the new generation of the National Strong‐Motion Observation Network System (NSMONS) of China were triggered. The NSMONS consists of 1154 permanent free‐field stations and began to operate in March 2008. The 2008 Wenchuan destructive earthquake triggered a large number of strong‐motion recordings that contribute significantly to the world strong‐motion database (Li, Zhou, Huang, et al. , 2008). The 2013 Lushan earthquake also provided a large number of near‐source recordings in China (Xie et al. , 2014). NSMONS aims to enhance the ability of earthquake monitoring and the collection of strong‐motion recordings in the most seismically active regions and some major cities in the Chinese mainland. As a result, its free‐field stations are irregularly distributed with an average spacing of 50 km to hundreds of kilometers (Li, Zhou, Yu, et al. , 2008). Thus, it definitely cannot monitor all of the seismic areas in China. For example, on 14 April 2010, the Yushu earthquake, which exhibited a magnitude of M s 7.1, occurred in the northeast part of the Tibetan plateau at Yushu, Qinghai Province. Only five strong‐motion stations of NSMONS were triggered, the nearest of which was approximately 350 km from the epicenter, and the maximum peak ground acceleration (PGA) was only approximately 2 cm/s2. Taking into account the randomness of the spatial distribution of earthquakes, most strong‐motion recordings obtained in recent years have small amplitudes and are thus not of interest to engineers (China Strong Motion Networks Center, 2012). As a result, these recordings only contribute to the steady growth of the strong‐motion …

Temporary strong-motion observation network for Wenchuan aftershocks and site classification

The Ms=8.0 (MW=7.9) Wenchuan earthquake of May 12, 2008 was the largest destructive event on the Chinese mainland since the 1976 Tangshan earthquake. Thousands of aftershocks occurred in the following months. To improve the performance of the National Strong-Motion Observation Network System (NSMONS) in China, a temporary strong-motion observation network was quickly set up along the Longmenshan Fault in the most heavily damaged areas. We briefly reviewed the history and the advances in temporary strong-motion observation in China where temporary networks have been proven to be a very effective way of accumulating strong-motion records from large aftershocks. Then the case of the Wenchuan earthquake was described together with the process of compiling, standardizing and disseminating the collected data. A total of 3250 records were collected from 92 temporary stations for 949 aftershocks between May 13 and October 10, 2008. The largest peak ground acceleration (PGA) is 966.5cm/s2 from an MS=4.2 earthquake on August 10, 2008. Some general statistics, such as the number of recorded events with various magnitudes, PGA and epicentral distance, were analyzed and compared with the data from permanent stations. These results show that the temporary network can effectively compensate for the large instrument spacing of the permanent network to record near-field ground motion. Since no borehole data are available for those temporary stations, their site classifications are inferred using a horizontal-to-vertical spectral ratio (HVSR) technique based on the observed strong-motion records. A scheme of six site classes is proposed to improve the reliability of the HVSR technique. As a result, the site classes of 66 temporary stations are recommended finally.

Site effects by generalized inversion technique using strong motion recordings of the 2008 Wenchuan earthquake

The generalized inversion of S-wave amplitude spectra from the free-field strong motion recordings of the China National Strong Motion Observation Network System (NSMONS) are used to evaluate the site effects in the Wenchuan area. In this regard, a total of 602 recordings from 96 aftershocks of the Wenchuan earthquake with magnitudes of M3.7-M6.5 were selected as a dataset. These recordings were obtained from 28 stations at a hypocenter distance ranging from 30 km to 150 km. The inversion results have been verified as reliable by comparing the site response at station 62WUD using the Generalized Inversion Technique (GIT) and the Standard Spectral Ratio method (SSR). For all 28 stations, the site predominant frequency Fp and the average site amplification in different frequency bands of 1.0–5.0 Hz, 5.0–10.0 Hz and 1.0–10.0 Hz have been calculated based on the inversion results. Compared with the results from the horizontal-to-vertical spectral ratio (HVSR) method, it shows that the HVSR method can reasonably estimate the site predominant frequency but underestimates the site amplification. The linear fitting between the average site amplification for each frequency band and the Vs20 (the average uppermost-20 m shear wave velocity) shows good correlation. A distance measurement called the asperity distance DAspt is proposed to reasonably characterize the source-to-site distance for large earthquakes. Finally, the inversed site response is used to identify the soil nonlinearity in the main shock and aftershocks of Wenchuan earthquake. In ten of the 28 stations analyzed in the main shock, the soil behaved nonlinearly, where the ground motion level is apparently beyond a threshold of PGA > 300 cm/s2 or PGV > 20 cm/s, and only one station coded 51SFB has evidence of soil nonlinear behavior in the aftershocks.

Model could explain high death toll of 2008 Wenchuan Earthquake

On 12 May 2008 the Wenchuan earthquake, a magnitude 7.9 event, killed nearly 70,000 people and displaced millions in western China. Drawing on the observations of the National Strong‐Motion Observation Network System (NSMONS), a network of 460 seismic detectors distributed throughout China, Zhang et al. calculated the details of the fault rupture process. The majority of previous research on the earthquake relied on remotely sensed or teleseismic observations. The NSMONS data used by the authors, on the other hand, were drawn from 26 strong‐motion sensors that were located within 20 to 120 kilometers of the ruptured fault.

Improved HVSR site classification method for free-field strong motion stations validated with Wenchuan aftershock recordings

Local site conditions play an important role in the effective application of strong motion recordings. In the China National Strong Motion Observation Network System (NSMONS), some of the stations do not provide borehole information, and correspondingly, do not assign the site classes yet. In this paper, site classification methodologies for free-field strong motion stations are reviewed and the limitations and uncertainties of the horizontal-to-vertical spectral ratio (HVSR) methods are discussed. Then, a new method for site classification based on the entropy weight theory is proposed. The proposed method avoids the head or tail joggle phenomenon by providing the objective and subjective weights. The method was applied to aftershock recordings from the 2008 Wenchuan earthquake, and 54 free-field NSMONS stations were selected for site classification and the mean HVSRs were calculated. The results show that the improved HVSR method proposed in this paper has a higher success rate and could be adopted in NSMONS.

Analysis of Horizontal Strong-Motion Attenuation in the Great 2008 Wenchuan Earthquake

A large number of strong-motion records were obtained by the National Strong-Motion Observation Network System (NSMONS) of China for the Wenchuan earthquake. There are 1350 components of strong-motion records from the mainshock at 455 stations. In these stations, 164 stations are located in the range of rupture dis- tance within 400 km and 37 stations are within 100 km. The largest peak ground acceleration is 957.8 Gal from the Wolong station in the hanging wall area with rup- ture distance of 23 km. The records from 164 stations in the range of rupture distance within 400 km are used in this study to investigate the hanging wall/footwall effects, directivity effects, and attenuation characteristics of ground motions from the Wenchuan earthquake. The characteristics of ground motion attenuations are com- pared in four subareas: hanging wall area, footwall area, forward directivity area, and backward directivity area. The study results show a clear hanging wall/footwall effect in near-fault ground motions within a rupture distance of 40 km, but it appears only in the peak ground acceleration and components at short periods below 1.0 s, and a strong forward directivity effect appears in ground motions over the whole range of rupture distance and period. Furthermore, the fitting attenuation curves of the peak ground acceleration and spectral accelerations of ground motions from the Wenchuan earthquake are compared with the predicted curves by an empirical attenuation model in the hanging wall and footwall areas.

Ground motion attenuation of MS8.0 Wenchuan earthquake

The great MS8.0 Wenchuan earthquake has been the most destructive earthquake since 1949 in China. The earthquake occurred no more than half a year after the establishment of the National Strong Motion Observation Network System (NSMONS) of China; what is more, the epicenter was located in the area with dense strong motion observation stations so that a large number of strong motion records of the main shock were obtained. In this paper, 501 strong motion records from 167 observation stations are utilized to establish the ground motion attenuation relations in three directions in the range of fault distance less than 600 km. The result shows the difference of seismic motion attenuation in two horizontal directions is insignificant. It is the first time that strong-motion records are used to establish the ground motion attenuation relations of the MS8.0 earthquake in China.

Preliminary site classification of free-field strong motion stations based on Wenchuan earthquake records

During the great Wenchuan earthquake, about 460 permanent free-field stations in National Strong Motion Observation Network System (NSMONS) of China captured the main shock acceleration records. These records can be applied to site effect analyses, and then the site classification of those permanent stations can be carried out firstly, which will served as the fundamental information for further research. In this paper, the site of near-fault stations is classified by horizontal-to-vertical spectral ratio (HVSR) method according to the site class description of Japan earthquake resistant design code and response spectral shapes (RSS) method following the site class description of the 1997 Uniform Building Code (UBC) provisions. Then based on the detailed borehole data of those free-field stations, the equivalent shear wave velocity and overburden thickness are calculated and the site classifications are given by Chinese code for seismic design of buildings. Furthermore, for the stations having successful microtremor test data, the site dominant periods are computed to verify the results of site classification. Finally, combined with all the above results, the recommended site classes of near-fault permanent free-field stations are given.

Strong motion observations and recordings from the great Wenchuan Earthquake

The National Strong Motion Observation Network System (NSMONS) of China is briefly introduced in this paper. The NSMONS consists of permanent free-field stations, special observation arrays, mobile observatories and a network management system. During the Wenchuan Earthquake, over 1,400 components of acceleration records were obtained from 460 permanent free-field stations and three arrays for topographical effect and structural response observation in the network system from the main shock, and over 20,000 components of acceleration records from strong aftershocks occurred before August 1, 2008 were also obtained by permanent free-field stations of the NSMONS and 59 mobile instruments quickly deployed after the main shock. The strong motion recordings from the main shock and strong aftershocks are summarized in this paper. In the ground motion recordings, there are over 560 components with peak ground acceleration (PGA) over 10 Gal, the largest being 957.7 Gal. The largest PGA recorded during the aftershock exceeds 300 Gal.

Preliminary Analysis of Strong-Motion Recordings from the Magnitude 8.0 Wenchuan, China, Earthquake of 12 May 2008

The number and density of strong-motion observation stations in mainland China was seriously behind the number in the United States, Japan, Iran, and Mexico prior to the year 2000 (Xie et al. 1982; Gao et al. 2001; Zhou 2006; Nozu 2004). The existing accelerograph network could not meet the needs of research, engineering, and construction in China. To improve the situation, the nation provided funds to implement construction of the National Strong Motion Observation Network System (NSMONS) of China in the 10th National Five-year Plan. The project considered the existing strong-motion stations, seismicity in all regions and cities, and the distribution of major engineering structures. It also considered the research and construction needs and trends to build the NSMONS. The network focuses on regional distribution of permanent stations, stations in major cities for rapid reporting of intensity, and special arrays for special research purposes, as shown in Figure 1. The network is augmented with mobile observations and includes the National Network Center and Regional Network Centers for record recovery, processing, and dissemination; and network technical support, management, and maintenance. The construction of NSMONS began in 2002 with five years of construction, trial operation, and inspection, and was put into formal operation in March 2008 (Earthquake Disaster Prevention and Mitigation Division of China Earthquake Administration 2008). During the Wenchuan, China, earthquake of 12 May 2008, the network system was fully operational and obtained records of the mainshock from about 460 permanent free-field stations and three arrays for topographical effect and structural response observation. After the mainshock, 59 mobile instruments were deployed in the hardest-hit areas to record motions of strong aftershocks. A large number of aftershock records have been obtained from these mobile instruments. The strong-motion records from the mainshock and aftershocks will provide basic data for …