A mobile marine seismometer(MMS)is a vertical underwater vehicle that detects ocean seismic waves.One of the critical operational requirements for an MMS is that it remains suspended at a desired depth.This article ai...A mobile marine seismometer(MMS)is a vertical underwater vehicle that detects ocean seismic waves.One of the critical operational requirements for an MMS is that it remains suspended at a desired depth.This article aimed to propose a fixed-depth suspension control for the MMS with a limited onboard energy supply.The research team established a kinematic model to analyze fluctuations in the vertical motion of the MMS and the delayed response of the system.We ascertained a direct one-to-one correlation between the displacement volume of the mobile ocean seismic instrument and the depth at which it reaches a state of neutral buoyancy(commonly referred to as the hover depth).A fixed-depth control algorithm was introduced,allowing a gradual approach to the necessary displacement volume to reach the desired suspension depth.The study optimized the boundary conditions to reduce unnecessary adjustments and mitigate the time delay caused by the instrument’s inertia,thereby significantly minimizing energy consumption.This method does not require calculating the hydrodynamic parameters or transfer functions of the MMS,thereby considerably reducing the implementation complexity.In the three-month sea trial in the South China Sea,the seismic instrument was set to hover at 800 m,with a permissible fluctuation of±100 m,operating on a seven-day cycle.The experimental results show that the seismic instrument has an average hover error of 34.6 m,with a vertical drift depth of 29.6 m per cycle,and the buoyancy adjustment system made six adjustments,indicating that our proposed control method performs satisfactorily.In addition,this method provides new insights for the fixed-depth control of other ocean observation devices that rely on buoyancy adjustment.展开更多
We report here the observation result of joint observation of long period tremor signals with broadband seismome-ter,tiltmeter and gravimeter at the HUST(Huazhong University of Science and Technology)station.The obser...We report here the observation result of joint observation of long period tremor signals with broadband seismome-ter,tiltmeter and gravimeter at the HUST(Huazhong University of Science and Technology)station.The observed data were compared and analyzed.Since 2005,the several tens of abnormal tremor signals which are weak,com-plex and duration of 2 to 3 days have been synchronously recorded by the different instruments.The tremor signals have the periodic domain in the range of 3 to 5 minutes,20 to 30 minutes and even more than 1 hour.The observa-tion shows such tremors are a physical existence.The analysis indicates that a part of the tremors caused by the typhoon from the western Pacific Ocean.These tremors have a close relationship with wind velocity of typhoon and distance between the typhoon center and the station.Except these,the cause of others is still unclear.展开更多
Using 1 Hz sampling records at one superconducting gravimeter （SG） station and 11 broadband seismometer stations, we found anomalous signals prior to the 2008 Wenchuan （汶川） earthquake event. The tides are remove...Using 1 Hz sampling records at one superconducting gravimeter （SG） station and 11 broadband seismometer stations, we found anomalous signals prior to the 2008 Wenchuan （汶川） earthquake event. The tides are removed from the original SG records to obtain the gravity residuals. Applying the Hilbert-Huang transform （HHT） and the wavelet analysis to the SG gravity residuals leads to time-frequency spectra, which suggests that there is an anomalous signal series around 39 h prior to the event. The period and the magnitude of the anomalous signal series are about 8 s and 3×10^-8 m/s^2 （3 μGal）, respectively. In another aspect, applying HHT analysis technique to 11 records at broadband seismometer stations shows that most of them contain anomalous signals prior to the Wenchuan event, and the marginal spectra of 8 inland stations show an apparent characteristic of double peaks in anomalous days compared to the only one peak of the marginal spectra in quiet days. Preliminary investigations suggest that the anomalous signals prior to the earthquake are closely related to the low-frequency earthquake （LFE）. We concluded that the SG data as well as the broadband seismometers records might be significant information sources in detecting the anomalous signals prior to large earthquakes.展开更多
Continuous seismic observations can record seismic waveforms, and ambient noise, for the purposes of earthquake researches and other applications. Here we deploy three digital seismometers(EPS-2) in and around the Nan...Continuous seismic observations can record seismic waveforms, and ambient noise, for the purposes of earthquake researches and other applications. Here we deploy three digital seismometers(EPS-2) in and around the Nanwangshan Campus of the China University of Geosciences(Wuhan). This network was running from April 9 to May 9 of 2018. During this period, the seismometers recorded the May 4, 2018 M6.9 Hawaii earthquake. From the recorded waveforms, we could observe clearly the P and S arrivals, and the corresponding particle motions. Analysis of continuous observations of ambient noise shows obvious fluctuation of vibration intensity inside of the campus. The campus is quietest from 0 to 5 am. From 5 am on, the vibration intensity increases, and reaches the peak of entire day at 12 am. The amplitude then decreases to a very low level at 19:30 to 20:00 pm, and reaches another strong noisy time at 21:00 to 21:30 pm. After 21:30 pm, the intensity goes down slowly. We also observed seismic signals that were generated by the interaction of speed-control hump cars and ground. By taking the envelope and smooth operations, we observe different characteristics for different car speeds, which suggests that seismic monitoring approaches can be used for speed measurement of cars. This kind of small seismic network running in a real time fashion, would greatly help understanding of the sources of ambient noise at high frequency bands in interested areas. Analysis of a long-term observed dataset, and real time illustration will help to strengthen campus security and high-precision laboratory deployments, and also contribute to research atmosphere in earthquake science.展开更多
The use of ocean bottom seismometers provides an effective means of studying the process and the dynamic of cold seeps by continuously recording micro-events produced by sub-seafloor fluid migration.We deployed a four...The use of ocean bottom seismometers provides an effective means of studying the process and the dynamic of cold seeps by continuously recording micro-events produced by sub-seafloor fluid migration.We deployed a four-component Ocean Bottom Seismometer(OBS)at an active site of the Haima cold seep from 6 November to 19 November in 2021.Here,we present the results of this short-term OBS monitoring.We first examine the OBS record manually to distinguish(by their distinctive seismographic signatures)four types of events:shipping noises,vibrations from our remotely operated vehicle(ROV)operations,local earthquakes,and short duration events(SDEs).Only the SDEs are further discussed in this work.Such SDEs are similar to those observed in other sea areas and are interpreted to be correlated with sub-seafloor fluid migration.In the OBS data collected during the 14-day monitoring period.We identify five SDEs.Compared to the SDE occurrence rate observed in other cold seep regions,five events is rather low,from which it could be inferred that fluid migration,and subsequent gas seepage,is not very active at the Haima site.This conclusion agrees with multi-beam and chemical observations at that site.Our observations thus provide further constraint on the seepage activity in this location.This is the first time that cold seep-related SDEs have been identified in the South China Sea,expanding the list of sea areas where SDEs are now linked to cold seep fluid migration.展开更多
Three-component Ocean Bottom Seismometers, portable land stations and marine air gun seismic sources were used to carry out an onshore-offshore deep seismic profile in northeastern South China Sea. This profile, orien...Three-component Ocean Bottom Seismometers, portable land stations and marine air gun seismic sources were used to carry out an onshore-offshore deep seismic profile in northeastern South China Sea. This profile, orientated in NNW-SSE, was as long as 500 km and perpendicular to the strike of regional tectonics. The offshore data were processed in Taiwan Ocean University using a number of available software and the onshore data were analyzed in South China Sea Institute of Oceanology by new-written programs and public software. Preliminary results show that the seismic data are in good quality and contain rich information of deep structure. Seismic phases, e.g. Pg, PmP and Pn, are identified in the offset range 5～220 kin, which will provide an important dataset for the deep crustal structure and oil-gas basin evolution studies of this region.展开更多
Seismometer self-noise levels were determined using Sleeman’s three-sensor method in combination with the Welch method for different parameter combinations. The self-noise levels decreased with the increasing segment...Seismometer self-noise levels were determined using Sleeman’s three-sensor method in combination with the Welch method for different parameter combinations. The self-noise levels decreased with the increasing segment window length, which is equivalent to the subwindow length, and with the increasing segment overlap rate for different frequency points at a fixed band. After the statistical examination of 9800 different parameter combinations, a zone of reasonable self-noise calculation parameter combinations was identified. Reasons for the unsuitability of certain parameter combinations were explored with respect to their distortion of the seismometer’s self-noise levels.展开更多
Longxi earthquake was the only earthquake example, which ZHANG Heng＇s Seismometer had detected. Therefore this event attracted the attention of the academic circle and also served as crucial evidence to examine the r...Longxi earthquake was the only earthquake example, which ZHANG Heng＇s Seismometer had detected. Therefore this event attracted the attention of the academic circle and also served as crucial evidence to examine the rationality of the reconstructed model of the seismometer. But for a long time, owing to the fact that the Jincheng-Longxi earthquake on February 28, AD 138 was mistaken as the event went against the historical records, it was refuted by the researches of both in China and abroad. By making careful textual research of historical records, especially by analyzing the description of Longxi earthquake of Houhan Shu, by studying the historical background exposed by historical literatures at that time, ZHANG Heng＇s biography, his poems and place names of Han Dynasty, by comparing five earthquakes occurred in Qing Dynasty and their attenuation of seismic intensity, the conclusion can be drawn that the Longxi earthquake should take place on December 13, AD 134 （the third year of Yangjia reign）. As a rough assessment, the epicenter was in Tianshui area and the magnitude was about 7. Due to the political corruption and inability to scientifically explain earthquake phenomenon at the end of Eastern Han Dynasty, a tragedy occurred during the later years of ZHANG Heng＇s life that had direct relations with the earthquake successively occurred in AD 133 and AD 134 after invention of seismometer in AD 132. In order to analyze the ground motion at Lingtai caused by the event in AD 134, the digital broad-band seismic records of three Longxi earthquakes in recent years recorded by Luoyang seismic station are used. The numerical modelings are made from three aspects of seismic magnitude definition, digital broad-band seismograms and empirical Green＇s function method. The results have shown that the maximum horizontal displacement at Lingtai is between 6-8 mm, and the maximum acceleration is less than 10^-2 m/s^2. These results have played an important role in quantitative test of the scientific reconstruction model of ZHANG Heng＇s Seismometer.展开更多
FBS-3A feedback broadband seismometer has been widely utilized in observation networks up to now. Therefore, it is very important and practically meaningful for the application of this kind of sensor to fulfill some r...FBS-3A feedback broadband seismometer has been widely utilized in observation networks up to now. Therefore, it is very important and practically meaningful for the application of this kind of sensor to fulfill some relative research work about its transfer function and for the analysis to the data recorded and the further development of the seismometer. In this paper, from the viewpoint of achieving its working principle, method of systematic analysis is applied to deduce the transfer functions, including both the transfer function for calibration and that for measurement. Moreover, on the basis of that, the distribution of its zeroes and poles in a complex frequency domain is analyzed, which provides a convincing evidence to simplify this seismometer system from a high-order one to a two-order one. And the emulation of the frequency characteristics of FBS-3A is presented in this paper. On the whole, the aim of this article is to do some theoretical work about the earthquake observation sensor, and also to introduce the method of making systematic analysis in a complex frequency domain to the research and the development of the seismometers.展开更多
First-arrival seismic traveltime tomography(FAST)is a well-established technique to estimate subsurface velocity structures.Although several existing open-source packages are available for first-arrival traveltime tom...First-arrival seismic traveltime tomography(FAST)is a well-established technique to estimate subsurface velocity structures.Although several existing open-source packages are available for first-arrival traveltime tomography,most were written in compiled languages and lack sufficient extendibility for new algorithms and functionalities.In this work,we develop an open-source,selfcontained FAST package based on MATLAB,one of the most popular interpreted scientific programming languages,with a focus on ocean bottom seismometer refraction traveltime tomography.Our package contains a complete traveltime tomography workflow,including ray-tracing-based first-arrival traveltime computation,linearized inversion,quality control,and high-quality visualization.We design the package as a modular toolbox,making it convenient to integrate new algorithms and functionalities as needed.At the current stage,our package is most efficient for performing FAST for two-dimensional ocean bottom seismometer surveys.We demonstrate the efficacy and accuracy of our package by using a synthetic data example based on a modified Marmousi model.展开更多
The intense deformation zone in the central Indian Ocean, south of Indian continent is one of the most complex regions in terms of its structure and geodynamics. The deformation zone has been studied and debated in 19...The intense deformation zone in the central Indian Ocean, south of Indian continent is one of the most complex regions in terms of its structure and geodynamics. The deformation zone has been studied and debated in 1990s for its genesis. It was argued that deformation is mainly confined to sedimentary and oceanic crustal layers, while the large wave length geoidal anomalies, on which the deformation region lies, called for deeper sources. The inter connection between deeper and the shallower sources is found missing. The current study focuses on the complexities of this region by analyzing OBS （ocean bottom seismometer） data. The data acquired by five OBS systems along a 300 km long south-north profile in the CIOB （central Indian Ocean basin） have been modeled and the crustal and sub-crustal structure has been determined using 2-D tomographic inversion. Four subsurface layers are identified representing the sediment column, upper crustal layer, lower crustal layer and a sub-crustal layer （upper mantle layer）. A considerable variation in thickness as well as velocity at all interfaces from sedimentary column to upper mantle is observed which indicates that the tectonic forces have affected the entire crust and sub-crustal configuration. The sediments are characterized by higher velocities （2.1 kin/s） due to the increased confining pressure. Modeling results indicated that the velocity in upper crust is in the range of 5.7-6.2 km/s and the velocity of the lower crust varies from 7.0-7.6 km/s. The velocity of the sub-crustal layer is in the range of 7.8-8.4 km/s. This high-velocity layer is interpreted as magmatic under-plating with strong lateral variations. The base of the 7.0 km/s layer at 12-15 km depth is interpreted as the Moho.展开更多
A seismometer data acquisition unit has been used in the Changping seismic station to record the output of a strainmeter. The output of a strainmeter was sampled at a rate of l00/sec by seismometer acquisition from th...A seismometer data acquisition unit has been used in the Changping seismic station to record the output of a strainmeter. The output of a strainmeter was sampled at a rate of l00/sec by seismometer acquisition from the original rate of 1 per minute. Plenty of high frequency sampled data was recorded. The minute value curve calculated from the seismometer acquisition are consistent with that of the original data sampled by the strain acquisition system. More complete waveforms were recorded with a higher sampling rate, and seismic phase parameters calculated by using higher sampling rate strain seismic waves are also in consistency with the results of its predecessors. Spectra of the strain seismic waves are compared with that of seismic waves recorded by a seismometer in the Shisanling seismic station, and their trends are almost the same. Besides, some lower frequency components still exist in strain seismic waves.展开更多
1 THE DEFICIENCY OF OBSERVATION TECHNIQUES ON STRONG NEARFIELD EARTHQUAKES Catastrophic earthquakes often result in huge loss on people s lives and property.Therefore,techniques concerning earthquake prevention and di...1 THE DEFICIENCY OF OBSERVATION TECHNIQUES ON STRONG NEARFIELD EARTHQUAKES Catastrophic earthquakes often result in huge loss on people s lives and property.Therefore,techniques concerning earthquake prevention and disaster reduction are closely related to citizens livelihood. It requires that seismologists master the mechanisms of seismic hazards,and perform timely w arning for earthquakes. Unfortunately.展开更多
We firstly detected the Earth's free toroidal oscillations excited by three large earthquakes in Japan,2011,Chile,2010 and Indonesia,2005 from the observed data of the JCZ-1 seismometer at Wuhan Seismic Station. T...We firstly detected the Earth's free toroidal oscillations excited by three large earthquakes in Japan,2011,Chile,2010 and Indonesia,2005 from the observed data of the JCZ-1 seismometer at Wuhan Seismic Station. The eigenperiods of basic modes (0T2 - 0T67 ) and first modes (1T2 ～ 1T50 ) were detected,and their error ratios were less than 0. 5% by comparing the observed eigenvalues with the theoretical eigenvalues in PREM. We supplemented some modes- 0T11,0T15 , 0T19 , 1T4 , 1T5 and 1T14 ,which were not mentioned in PREM,and also observed the spectral line multi-peak phenomenon from 0T2, 0T6 , 0T7 and 0T8 . These results show that the JCZ-1 seismometer is able to precisely observe the Earth's long period toroidal free oscillations.展开更多
基金The National Key Research and Development Program of China under contract Nos.2021YFC3101401 and 2022YFC3003802the Deep Blue Fund under contract No.SL2103+2 种基金the Zhejiang Provincial Key Research and Development Program under contract No.2021C03186the Zhejiang Provincial Natural Science Foundation of China under contract No.LDQ24D060001the Open Fund Project of Key Laboratory of Ocean Observation Technology,MNR under contract No.2024klootA11.
文摘A mobile marine seismometer(MMS)is a vertical underwater vehicle that detects ocean seismic waves.One of the critical operational requirements for an MMS is that it remains suspended at a desired depth.This article aimed to propose a fixed-depth suspension control for the MMS with a limited onboard energy supply.The research team established a kinematic model to analyze fluctuations in the vertical motion of the MMS and the delayed response of the system.We ascertained a direct one-to-one correlation between the displacement volume of the mobile ocean seismic instrument and the depth at which it reaches a state of neutral buoyancy(commonly referred to as the hover depth).A fixed-depth control algorithm was introduced,allowing a gradual approach to the necessary displacement volume to reach the desired suspension depth.The study optimized the boundary conditions to reduce unnecessary adjustments and mitigate the time delay caused by the instrument’s inertia,thereby significantly minimizing energy consumption.This method does not require calculating the hydrodynamic parameters or transfer functions of the MMS,thereby considerably reducing the implementation complexity.In the three-month sea trial in the South China Sea,the seismic instrument was set to hover at 800 m,with a permissible fluctuation of±100 m,operating on a seven-day cycle.The experimental results show that the seismic instrument has an average hover error of 34.6 m,with a vertical drift depth of 29.6 m per cycle,and the buoyancy adjustment system made six adjustments,indicating that our proposed control method performs satisfactorily.In addition,this method provides new insights for the fixed-depth control of other ocean observation devices that rely on buoyancy adjustment.
文摘We report here the observation result of joint observation of long period tremor signals with broadband seismome-ter,tiltmeter and gravimeter at the HUST(Huazhong University of Science and Technology)station.The observed data were compared and analyzed.Since 2005,the several tens of abnormal tremor signals which are weak,com-plex and duration of 2 to 3 days have been synchronously recorded by the different instruments.The tremor signals have the periodic domain in the range of 3 to 5 minutes,20 to 30 minutes and even more than 1 hour.The observa-tion shows such tremors are a physical existence.The analysis indicates that a part of the tremors caused by the typhoon from the western Pacific Ocean.These tremors have a close relationship with wind velocity of typhoon and distance between the typhoon center and the station.Except these,the cause of others is still unclear.
基金supported by the National Natural Science Foundation of China (Nos. 40974015, 40637034)the Research Program for Outstanding Doctoral Candidates of Wuhan University (No. 2008-50)
文摘Using 1 Hz sampling records at one superconducting gravimeter （SG） station and 11 broadband seismometer stations, we found anomalous signals prior to the 2008 Wenchuan （汶川） earthquake event. The tides are removed from the original SG records to obtain the gravity residuals. Applying the Hilbert-Huang transform （HHT） and the wavelet analysis to the SG gravity residuals leads to time-frequency spectra, which suggests that there is an anomalous signal series around 39 h prior to the event. The period and the magnitude of the anomalous signal series are about 8 s and 3×10^-8 m/s^2 （3 μGal）, respectively. In another aspect, applying HHT analysis technique to 11 records at broadband seismometer stations shows that most of them contain anomalous signals prior to the Wenchuan event, and the marginal spectra of 8 inland stations show an apparent characteristic of double peaks in anomalous days compared to the only one peak of the marginal spectra in quiet days. Preliminary investigations suggest that the anomalous signals prior to the earthquake are closely related to the low-frequency earthquake （LFE）. We concluded that the SG data as well as the broadband seismometers records might be significant information sources in detecting the anomalous signals prior to large earthquakes.
基金the National Key R&D Program of China(No.2018YFC0603500)Programme on Global Change and Air-Sea Interaction(No.GASI-GEOGE-02)+1 种基金NSFC(Nos.41474050,41874062)one of the outcomes of the research projects(No.Q20203004),analysis of campus ambient noise monitored by short-seismometers funded by Scientific Research Foundation of the Education Department of Hubei Province,China。
文摘Continuous seismic observations can record seismic waveforms, and ambient noise, for the purposes of earthquake researches and other applications. Here we deploy three digital seismometers(EPS-2) in and around the Nanwangshan Campus of the China University of Geosciences(Wuhan). This network was running from April 9 to May 9 of 2018. During this period, the seismometers recorded the May 4, 2018 M6.9 Hawaii earthquake. From the recorded waveforms, we could observe clearly the P and S arrivals, and the corresponding particle motions. Analysis of continuous observations of ambient noise shows obvious fluctuation of vibration intensity inside of the campus. The campus is quietest from 0 to 5 am. From 5 am on, the vibration intensity increases, and reaches the peak of entire day at 12 am. The amplitude then decreases to a very low level at 19:30 to 20:00 pm, and reaches another strong noisy time at 21:00 to 21:30 pm. After 21:30 pm, the intensity goes down slowly. We also observed seismic signals that were generated by the interaction of speed-control hump cars and ground. By taking the envelope and smooth operations, we observe different characteristics for different car speeds, which suggests that seismic monitoring approaches can be used for speed measurement of cars. This kind of small seismic network running in a real time fashion, would greatly help understanding of the sources of ambient noise at high frequency bands in interested areas. Analysis of a long-term observed dataset, and real time illustration will help to strengthen campus security and high-precision laboratory deployments, and also contribute to research atmosphere in earthquake science.
基金supported by the Key Research and Development Project of Guangdong Province(Grant:2020B1111510001)supported by the Project of Sanya Yazhou Bay Science and Technology City(Grant No:SCKJ-JYRC-2022-14)the National Natural Science Foundation of China(Grant No:92262304).
文摘The use of ocean bottom seismometers provides an effective means of studying the process and the dynamic of cold seeps by continuously recording micro-events produced by sub-seafloor fluid migration.We deployed a four-component Ocean Bottom Seismometer(OBS)at an active site of the Haima cold seep from 6 November to 19 November in 2021.Here,we present the results of this short-term OBS monitoring.We first examine the OBS record manually to distinguish(by their distinctive seismographic signatures)four types of events:shipping noises,vibrations from our remotely operated vehicle(ROV)operations,local earthquakes,and short duration events(SDEs).Only the SDEs are further discussed in this work.Such SDEs are similar to those observed in other sea areas and are interpreted to be correlated with sub-seafloor fluid migration.In the OBS data collected during the 14-day monitoring period.We identify five SDEs.Compared to the SDE occurrence rate observed in other cold seep regions,five events is rather low,from which it could be inferred that fluid migration,and subsequent gas seepage,is not very active at the Haima site.This conclusion agrees with multi-beam and chemical observations at that site.Our observations thus provide further constraint on the seepage activity in this location.This is the first time that cold seep-related SDEs have been identified in the South China Sea,expanding the list of sea areas where SDEs are now linked to cold seep fluid migration.
基金Supported by SCSIO(LYQY200302)the Chinese Ministry of Science and Technology(G2000046701)+2 种基金the Guangdong Department of Science and Technology(2002C32604)the Guangdong Natural Science Foundation(021557)the National Natural Science Foundation of China(4000161958).
文摘Three-component Ocean Bottom Seismometers, portable land stations and marine air gun seismic sources were used to carry out an onshore-offshore deep seismic profile in northeastern South China Sea. This profile, orientated in NNW-SSE, was as long as 500 km and perpendicular to the strike of regional tectonics. The offshore data were processed in Taiwan Ocean University using a number of available software and the onshore data were analyzed in South China Sea Institute of Oceanology by new-written programs and public software. Preliminary results show that the seismic data are in good quality and contain rich information of deep structure. Seismic phases, e.g. Pg, PmP and Pn, are identified in the offset range 5～220 kin, which will provide an important dataset for the deep crustal structure and oil-gas basin evolution studies of this region.
基金supported by Study on Seismograph Calibration and Preparation of Draft International Standard (201408005)the Earthquake Science and technology Program of Hebei Province (201303)Special Program for Earthquake monitoring (20130203)
文摘Seismometer self-noise levels were determined using Sleeman’s three-sensor method in combination with the Welch method for different parameter combinations. The self-noise levels decreased with the increasing segment window length, which is equivalent to the subwindow length, and with the increasing segment overlap rate for different frequency points at a fixed band. After the statistical examination of 9800 different parameter combinations, a zone of reasonable self-noise calculation parameter combinations was identified. Reasons for the unsuitability of certain parameter combinations were explored with respect to their distortion of the seismometer’s self-noise levels.
基金Joint Seismological Science Foundation of China (104133)
文摘Longxi earthquake was the only earthquake example, which ZHANG Heng＇s Seismometer had detected. Therefore this event attracted the attention of the academic circle and also served as crucial evidence to examine the rationality of the reconstructed model of the seismometer. But for a long time, owing to the fact that the Jincheng-Longxi earthquake on February 28, AD 138 was mistaken as the event went against the historical records, it was refuted by the researches of both in China and abroad. By making careful textual research of historical records, especially by analyzing the description of Longxi earthquake of Houhan Shu, by studying the historical background exposed by historical literatures at that time, ZHANG Heng＇s biography, his poems and place names of Han Dynasty, by comparing five earthquakes occurred in Qing Dynasty and their attenuation of seismic intensity, the conclusion can be drawn that the Longxi earthquake should take place on December 13, AD 134 （the third year of Yangjia reign）. As a rough assessment, the epicenter was in Tianshui area and the magnitude was about 7. Due to the political corruption and inability to scientifically explain earthquake phenomenon at the end of Eastern Han Dynasty, a tragedy occurred during the later years of ZHANG Heng＇s life that had direct relations with the earthquake successively occurred in AD 133 and AD 134 after invention of seismometer in AD 132. In order to analyze the ground motion at Lingtai caused by the event in AD 134, the digital broad-band seismic records of three Longxi earthquakes in recent years recorded by Luoyang seismic station are used. The numerical modelings are made from three aspects of seismic magnitude definition, digital broad-band seismograms and empirical Green＇s function method. The results have shown that the maximum horizontal displacement at Lingtai is between 6-8 mm, and the maximum acceleration is less than 10^-2 m/s^2. These results have played an important role in quantitative test of the scientific reconstruction model of ZHANG Heng＇s Seismometer.
文摘FBS-3A feedback broadband seismometer has been widely utilized in observation networks up to now. Therefore, it is very important and practically meaningful for the application of this kind of sensor to fulfill some relative research work about its transfer function and for the analysis to the data recorded and the further development of the seismometer. In this paper, from the viewpoint of achieving its working principle, method of systematic analysis is applied to deduce the transfer functions, including both the transfer function for calibration and that for measurement. Moreover, on the basis of that, the distribution of its zeroes and poles in a complex frequency domain is analyzed, which provides a convincing evidence to simplify this seismometer system from a high-order one to a two-order one. And the emulation of the frequency characteristics of FBS-3A is presented in this paper. On the whole, the aim of this article is to do some theoretical work about the earthquake observation sensor, and also to introduce the method of making systematic analysis in a complex frequency domain to the research and the development of the seismometers.
基金financially supported by the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (Grant No. GML2019 ZD0207)supported by the Guangzhou Municipal Science and Technology Bureau (Grant No. 202102021054)
文摘First-arrival seismic traveltime tomography(FAST)is a well-established technique to estimate subsurface velocity structures.Although several existing open-source packages are available for first-arrival traveltime tomography,most were written in compiled languages and lack sufficient extendibility for new algorithms and functionalities.In this work,we develop an open-source,selfcontained FAST package based on MATLAB,one of the most popular interpreted scientific programming languages,with a focus on ocean bottom seismometer refraction traveltime tomography.Our package contains a complete traveltime tomography workflow,including ray-tracing-based first-arrival traveltime computation,linearized inversion,quality control,and high-quality visualization.We design the package as a modular toolbox,making it convenient to integrate new algorithms and functionalities as needed.At the current stage,our package is most efficient for performing FAST for two-dimensional ocean bottom seismometer surveys.We demonstrate the efficacy and accuracy of our package by using a synthetic data example based on a modified Marmousi model.
文摘The intense deformation zone in the central Indian Ocean, south of Indian continent is one of the most complex regions in terms of its structure and geodynamics. The deformation zone has been studied and debated in 1990s for its genesis. It was argued that deformation is mainly confined to sedimentary and oceanic crustal layers, while the large wave length geoidal anomalies, on which the deformation region lies, called for deeper sources. The inter connection between deeper and the shallower sources is found missing. The current study focuses on the complexities of this region by analyzing OBS （ocean bottom seismometer） data. The data acquired by five OBS systems along a 300 km long south-north profile in the CIOB （central Indian Ocean basin） have been modeled and the crustal and sub-crustal structure has been determined using 2-D tomographic inversion. Four subsurface layers are identified representing the sediment column, upper crustal layer, lower crustal layer and a sub-crustal layer （upper mantle layer）. A considerable variation in thickness as well as velocity at all interfaces from sedimentary column to upper mantle is observed which indicates that the tectonic forces have affected the entire crust and sub-crustal configuration. The sediments are characterized by higher velocities （2.1 kin/s） due to the increased confining pressure. Modeling results indicated that the velocity in upper crust is in the range of 5.7-6.2 km/s and the velocity of the lower crust varies from 7.0-7.6 km/s. The velocity of the sub-crustal layer is in the range of 7.8-8.4 km/s. This high-velocity layer is interpreted as magmatic under-plating with strong lateral variations. The base of the 7.0 km/s layer at 12-15 km depth is interpreted as the Moho.
基金sponsored by Central Public-interest Scientific Institution Basic Research Fund of Institute of Crustal Dynamics,CEA(ZDJ2008-40,ZDJ2010-15)
文摘A seismometer data acquisition unit has been used in the Changping seismic station to record the output of a strainmeter. The output of a strainmeter was sampled at a rate of l00/sec by seismometer acquisition from the original rate of 1 per minute. Plenty of high frequency sampled data was recorded. The minute value curve calculated from the seismometer acquisition are consistent with that of the original data sampled by the strain acquisition system. More complete waveforms were recorded with a higher sampling rate, and seismic phase parameters calculated by using higher sampling rate strain seismic waves are also in consistency with the results of its predecessors. Spectra of the strain seismic waves are compared with that of seismic waves recorded by a seismometer in the Shisanling seismic station, and their trends are almost the same. Besides, some lower frequency components still exist in strain seismic waves.
基金sponsored by National Natural Science Foundation of China(41861134009)。
文摘1 THE DEFICIENCY OF OBSERVATION TECHNIQUES ON STRONG NEARFIELD EARTHQUAKES Catastrophic earthquakes often result in huge loss on people s lives and property.Therefore,techniques concerning earthquake prevention and disaster reduction are closely related to citizens livelihood. It requires that seismologists master the mechanisms of seismic hazards,and perform timely w arning for earthquakes. Unfortunately.
基金sponsored by the Key Program of National Natural Science Foundation of China ( 40730317)
文摘We firstly detected the Earth's free toroidal oscillations excited by three large earthquakes in Japan,2011,Chile,2010 and Indonesia,2005 from the observed data of the JCZ-1 seismometer at Wuhan Seismic Station. The eigenperiods of basic modes (0T2 - 0T67 ) and first modes (1T2 ～ 1T50 ) were detected,and their error ratios were less than 0. 5% by comparing the observed eigenvalues with the theoretical eigenvalues in PREM. We supplemented some modes- 0T11,0T15 , 0T19 , 1T4 , 1T5 and 1T14 ,which were not mentioned in PREM,and also observed the spectral line multi-peak phenomenon from 0T2, 0T6 , 0T7 and 0T8 . These results show that the JCZ-1 seismometer is able to precisely observe the Earth's long period toroidal free oscillations.
