The Timor Trough is located at the boundary of the Eurasian and the Australian plates， in the outer Banda Arc between the Banda Sea in Southeast Asia and the Timor Sea in northwest Australia. Since the Neogene， especially from the Late Miocene to the Late Pliocene， the collision between the Australian continent and the Banda Arc caused the uplift of Timor Island and the deformation of the Timor Trough， which affected the regional tectonic activities. A series of normal faults developed at the margin of the Australian Northwest shelf， which mainly controls the platform， horst， and graben features. The northern Timor Trough formed a series of thrust faults under the dual effect of the uplift of Timor Island and subsidence of the Timor Trough caused by arc continental collision. The NE-SW thrust fault at the bottom of the Timor Trough is the deformation front that controls the shape of the trough. The characteristics of tectonics and earthquakes indicate that the Banda subduction zone between the Australian Plate and Banda Arc is located in the Ombai Strait， which is between Timor Island and the inner Banda Arc， subducting at an average high angle of approximately 62° at a depth of more than 600 km. The subduction angle in the south is larger than that in the north， which is related to the compression of the Indian Ocean subduction plate. The front oceanic crust subducted below the northwest Banda Sea showed a horizontal trend below 500 km. There is an obvious discontinuity in the earthquakes between the deep and upper focus zones. The subduction of the Australian Plate beneath the Southeast Asian Plate may have gradually slowed down and stopped； however， the deformation of Timor Island and the Timor Trough caused by arc continental collision continues. The inner Banda Arc is deforming along the Banda Sea. Under the background of relatively balanced subduction， the subduction of the Australian Plate beneath the Southeast Asian Plate may have transformed into an orogeny. In the future， the inner Banda Arc may be uplifted to form an inner and outer Banda Arc double orogenic belt.
The process of earthquake incubation is accompanied by tectonic movement， material migration and density changes， which will cause changes in the Earth's gravity field. Repeated observations of flowing gravity may capture precursor information related to earthquake incubation， thereby providing important basis for mid- and short-term earthquake prediction. Based on the relative gravity observation data of the North-South seismic belt from 2017 to 2020， this paper obtains the spatio-temporal changes of the regional gravity field in southeastern Gansu， and analyzes the dynamic changes of the regional gravity field and its relationship with the occurrence of the Xiahe MS 5.7 earthquake in Gansu in 2019. The results show that： ① The contour of the gravity anomaly change in the observation area before the earthquake is basically the same as the strike of the Lintan-Tanchang fault， and the four-quadrant distribution characteristics appear near the epicenter. The Xiahe MS 5.7 earthquake occurred in the high gradient zone and near the center of the four-quadrant. ② The regional gravity field before and after the earthquake experienced a spatiotemporal evolution process of "regional gravity anomaly-four-quadrant distribution characteristics-reverse change earthquake". ③ The occurrence of the Jiuzhaigou earthquake may cause the adjustment of the stress field in the nearby fault area， thus accelerating the occurrence of the Xiahe earthquake. ④ The time-varying regional gravity field corresponds well to the Lintan-Tanchang fault in space. Comprehensive analysis can be considered that the seismogenic fault of this earthquake is the Lintan-Tanchang fault.
Himalayan orogenic belt is the highest and largest continental collision and subduction zone on the Earth. The Himalayan orogenic belt has produced frequent large earthquakes and caused several geohazards due to landslides and housing collapse, having an impact on the safety of life and property along a length of over 2500 km. Here we took three earthquake clusters as examples, which occurred at Nepal Himalaya, eastern Himalayan syntaxis and western Himalayan syntaxis, respectively. Here we calculated the earthquake locations and fault plane solutions based on the waveform data recorded by seismic stations deployed in source areas by the Institute of Tibetan Plateau Research, Chinese Academy of Sciences. We found that at the Nepal Himalayan, the Main Himalayan Thrust is the major tectonic structure for large earthquakes to occur. At the eastern Himalayan syntaxis, most earthquakes are of the reverse or strike-slip faulting. The major tectonic feature is the combination of the NE-dipping thrust with the southeastern escape of the Tibetan plateau. At the western Himalayan syntaxis, intermediate-depth earthquakes are active. These observations reveal the geometry of the deep subduction of the continental plate with steep dipping angle.
”Deep well, wide band, multi-component comprehensive observation” is the development direction of seismic observation. In order to promote the application and development of underground integrated observation system, key technologies, such as high temperature resistance sensor, interference isolation of sensor unit and miniaturization of instrument, need to be developed. Optic fiber sensors have the advantages of small size, passive nature, resistance to electromagnetic interference, being easy to long distance transmission and multi-parametric network observation, which are expected to provide new technology for the comprehensive observation of multi-parameter earthquakes in deep wells. This paper proposed a comprehensive observation technique of seismic wave, crustal deformation and temperature. An integrated borehole seismic sensor based on fiber Bragg grating resonators was designed for measuring three-component earthquake, three-component crustal deformation and temperature signal. A new technique for simultaneous measurement of multi-parameters of temperature and strain of fiber based on effective cavity length was presented. The technique of high precision optical fiber signal demodulation based on single side band sweep laser and the design of multi-parameter integrated optical fiber probe were introduced. The resolution of strain and temperature measurement of the fiber multi-parameter sensor system reached 4.7 × 10-10 and 6×10-5 ℃ , respectively. A comprehensive multi-parameter earthquake observation experiment was carried out at the seismic station. The results show that the integrated optical fiber multi-parameter seismic observation system can simultaneously record the earth tide signal, seismic wave signal and environmental temperature disturbance, and has good anti-environmental interference ability and long-term stability, which is expected to provide a new technique for crustal deformation observation.
The mechanism of earthquake inoculation and the process of earthquake occurrence are very complicated. Additionally, earthquakes do not happen very often, and we lack enough cognition to the earth’s interior structure, activity regularity and other key elements. As a result, research progress about the theory of earthquake precursors has been greatly restricted. Ground gravity observation has become one of the main ways to study earthquake precursor information in many countries and regions. This paper briefly summarized the surface gravity observation technology and observation network in China: the surface gravity measurement instrument developed from Huygens physical pendulum in seventeenth Century to today’s high-precision absolute gravimeter, and its accuracy reached to ±1×10-8 m/s2. China has successively established the National Gravity Network, Digital Earthquake Observation Network of China,the Crustal Movement Observation Network of China Ⅰ and the Crustal Movement Observation Network of China, to provide a public platform for monitoring non tidal gravity change, seismic gravity and tectonic movement. The use of specific examples illustrated the role of gravity observation data in earthquake prediction. The gravity observation data of ground gravity can be used to capture the information of gravity change in the process of strong earthquake inoculation, and to provide an important basis for the long-term prediction of strong earthquakes. The temporal and spatial variation characteristics of the regional gravity field and its relation to strong earthquakes were analyzed: Before the earthquake whose magnitude is higher than MS 5, generally there will be a large amplitude and range of gravity anomaly zones. Strong earthquakes occur mainly in areas where the gravity field changes violently. The dynamic change images of gravity field can clearly reflect the precursory information of large earthquakes during the inoculation and occurrence. Finally, the existing problems of surface gravity technology in earthquake precursor observation were put forward and the use of gravity measurement data in earthquake prediction research was prospected.
The hydrochemical types and origins of underground water in Songyuan and vicinity, Liaoning Province were discussed based on the hydrochemical composition, δD and δ18O. The water samples from eight wells were collected 4 times during 2014 to 2015. The main ion concentrations of water were analyzed with an Ion Chromatography. Isotopic compositions of hydrogen and oxygen were analyzed with the Liquid Water Isotope Analyzer. The mineralization (TDS) of the water ranged from 125.4 mg/L to 19 350.9 mg/L. Values of δD and δ18O ranged from -71.7‰ to -98.1‰ and from -9.0‰ to -12.5‰, respectively. The isotopic data indicated that the water originated from meteorological precipitation. The chemical compositions of Taolaizhao phreatic water were influenced by the human activity while the other water samples collected from artesian well were less affected by the human activity. Water in Changling, Dongdashi, Taohaotai, Qianan and Ningjiang were characterized by HCO3-Na with low TDS values. Such chemical types of water with fluctuations of Na+, S O 4 2 - and δ18O drift were resulted from dissolving silicate minerals and adding surfactant during oil exploitation. Fresh water in Fuyu well was Cl-Na type, which was influenced by acid injection during oil exploitation. Water in Qianguo well was characterized by Cl-Na type with TDS up to 19 350.9 mg/L, the obvious fluctuations of hydrogen and oxygen isotopes and increasing ion concentrations in the Qianguo well may be caused by the earthquakes that occurred in the sampling duration. The results will provide the background of hydrochemistry, and will be of benefit to monitoring earthquake and certificating seismic-chemical anomalies in the future.
Degassing of Hydrogen (H2) from fault may be a good indicator of fault activity. The concentration of H2 in soil gas in the seismic surface rupture zone produced by the Wenchuan MS 8.0 earthquake was investigated in twenty three measuring regions in order to explore the relationship between the spatio-temporal variations of H2 concentration in soil gas along the seismic rupture zone and the vertical displacements and aftershocks activities. The results indicated: ① the sources of H2 were directly related to from the release of natural gas reservoirs; ②the average concentration of H2 in soil gas spatially decreased from Yingxiu to Nanba; ③the magnitudes of the H2 concentration anomalies declined significantly with time. It is very significant to study the variation tendency of atmospheric environment with further research of degassing of H2 from faults.
Marine sedimentary basin is an important tectonic unit in the earth, and the evolution of marine sedimentary basin involves a series of the coupling and evolution of geodynamic mechanism such as the crust-mantle, the lithosphere-asthenosphere, the strata-fluid deposition. Therefore, the study of marine sedimentary basin dynamics includes deep structure state of earth, material composition and regional tectonic evolution, and also internal structure, tectonic characteristics and pore fluid characteristics strata of the basin. Wide angle Ocean Bottom Seismometer (OBS) seismic exploration is a marine geophysical survey method originated and developed since 1980’s and 1990’s, which has the advantages of strong penetration capability, high seismic imaging precision and reception of both P-wave and S-wave, and playing an increasing significant role in the research of marine sedimentary basin at the aspect of regional tectonic evolution, internal structure and pore fluid development characteristics of strata in recent years. In the study of passive continental margin, the crustal structure acquired from wide angle OBS seismic data provides the direct evidence that divides the passive continental margins into magma-poor and magma-dominated ones, and the degree of thinning and spatial variation characteristics of crust provide constraints for dynamics simulations of tectonic evolution in marine sedimentary basin. In the study of the structure features of basin, wide angle OBS seismic exploration fills in gaps at the aspect of investigation depth and complex geological structure in conventional multi-channel seismic survey, and acquires overpressure distribution status of basin according to the velocity structure characteristics of strata, and then infer the basin sedimentation velocity and pore fluid characteristics. In the study of internal fluid system in marine sedimentary basin, it reveals the velocity structure of natural gas hydrate reservoir through the analysis and processing of wide angle OBS seismic data, and calculates the thickness of natural gas hydrate reservoir and the content of hydrate and free gas in pore based on the velocity variation. Of course, the future wide angle OBS seismic exploration in the aspect of dynamic evolution and mechanism research in marine sedimentary basin will play a more important role with the development of marine seismic exploration technology, the improvement of data processing and instrument parameters.
the Kalpin nappe is an important multiple thrust system. It is important to study the Cenozoic tectonic of the Tianshan Mountain. Holocene active characteristics and paleoearthquake of the Kalpin nappe can be used to evaluate the neotectonic of this area. In this paper, we accurately measured the fault scarp in the front of three thrust-fold faults and analyzed paleoearthquake events in the trenches of the Kalpin nappe. Using the 10Be exposure age, we obtained those geomorphic surface ages and paleoearthquake times. The result showed that the slip rates of the west Kalpintag fault, aozitag fault and the tuoketag fault were 1.45(+1.68/-0.44) mm/a, 0.81(+0.35/-0.19) mm/a and (0.3±0.05) mm/a, respectively since the Holocene. The slip rate indicated that the increased activity transferred from back-row fault to front-row fault and accorded with the piggy-back propagation model in the Tianshan Mountain. Displacements and recurrence intervals of paleoearthquakes was similar to the slip rate characteristics. It also showed paleoearthquakes in the front row fault were stronger than paleoearthquakes of the back row fault. The strong paleoearthquake which caused the highest surface rupture happened in the Kalpintag fault. The interval of paleoearthquakes was about 4 ka and the displacement of every paleoearthquake was about 3 m in the west Kalpintag fault; the interval of paleoearthquakes was about 2 ka and the displacement of every paleoearthquake was about 1m in the aozitag fault; the tuoketag fault ruptured only one paleoearthquake since 7 ka. The Piqiang tear fault was the tectonic result of different shortening rate between the west Kalpin system and the east Kalpin system. The shortening rate of west Kalpin system was obviously stronger than the east Kalpin system. The huge separation distance was near 20 km between the east and the west back-row fault. Because the slip rate of system transferred to the front-row fault in the piggy-back propagation model, the separation distance (~4 km) between the east and the west front-row fault was increasing.
The affecting factors on gas geochemical characteristics extracted from hyper-spectral data in the Zhangjiakou-Bohai seismic zone were discussed. Temporal and spatial variations of total column CO and CH4 were analyzed based on the satellite hyper-spectral data. Temporally, the total column CO in the study area showed obviously seasonal variation, while CH4 didn't. Spatially, values of total column CO and CH4 in the southern part of the study area were higher than thoes in the northern part. Both total column CO and CH4 increased from western to eastern, and showed the largest changing rate over the piedmont fault zone at the junction of plain and mountains. The temporal variations of total CO and CH4 backgrounds could be attributed to the effects of climate and weather. The spatial variations of total CO and CH4 backgrounds may be controlled by the regional topography, geology, seismic activities, crustal thickness and so on. The results not only provide new scientific data for monitoring earthquake, but also have an important significance to the study of earthquake anomaly identification and segmentation seismic activity of fault zone.
For the case of seismic waves in a more complex architecture porous medium wave field occurs slightly changed with changes in the structure, several parameters characteristics of the structure of the media which influence on various types of seismic wave propagation were studied. Firstly, the article establishes the isotropic elastic porous medium model, derive the corresponding elastic wave equation, and uses high-order staggered-grid finite difference method for forward modeling, the article also analyze the pore structure parameters such as porosity, viscosity and penetration influence on the wave field characteristics were also analyzed. At the same time, the study analyze the influence of porosity, permeability and viscosity on phase velocity and attenuation coefficient was analyzed in the stady. The results showed that the influence on attenuation coefficient was more sensitive than that on phase velocity. This study helps to deepen the understanding of seismic wave propagation in the practical system of complex medium.
Carbon Capture and Storage (CCS) technology is currently recognized as the most effective way to mitigate greenhouse gas. CO2 geological storage is the key technique in CCS, and monitoring the safety of CO2 geological storage runs through the whole CCS project from CO2 injection and after closure. 4D seismic monitoring technique is the most effective way to monitor the leakage of CO2 and to confirm the safety of CO2 sequestration. Traditional 4D seismic technology predicts saturation of CO2 and pressure distribution in reservoir by comparing two vintages seismic amplitude and travel time from two or repeated 3D seismic data before and after CO2 injection or between two different injection stages. 4D multicomponent seismic monitoring has a great potential to be explored. Because shear wave velocity is sensitive to pressure, we may discriminate pore pressure distribution by using 4D multicomponent seismic information. For anisotropy reservoir, we may confirm the change of reservoir fissures and fractures as well as reservoir and caprock stress status before and after CO2 injection through comparing difference of travel time and amplitude of PS1 and PS2 wave in two vintages seismic acquisition. Furthermore, we will find out potential CO2 leakage risk area more accurately and evaluate the safety of CO2 sequestration more reliablely by combining rock physics experiment and dipole sonic log data with 4D multicomponent seismic monitoring.
The principle of satellite hyperspectral remote sensing technique for atmosphere detection, development of the satellite atmospheric infrared sensors and the retrieval method of gaseous components with hyperspectral remote sensing data were briefly reviewed. The application of hyperspectral remote sensing gas-geochemistry in earthquake monitoring was emphasized, which can be divided into two aspects: ①Degassing from the seismic fracture zone was indirectly retrieved with the thermal infrared sensor; ②Gas-geochemical anomaly associated with the earthquake was directly detected by the atmospheric gas sensors. Gas-geochemical anomalies were obtained by correlating the physical and chemical anomalies caused by gas emission from the underground with the seismic activities. The possible mechanism of anomalies was discussed by analyzing the gas-geochemical anomalies related to the typical earthquake cases. Additionally, the developing aspects in seismic remote-sensing for gas-geochemistry were proposed.
CO2 capture and storage projects must consider the potential possibility ofinjection induced seismicity. Moderate earthquakes and strong earthquakes may endanger human life and property, and even felt earthquakes and microquakes also pose a threat to seal integrity of CO2 reservoir and increase the risk of leakage. Underground fluid injection induced seismicity usually happens in some geoengineering projects such as waste fluid disposal, EOR and EGS, and it occurs when fluid is injected along the fault. Therefore, it can be studied through stress analysis. The density of supercritical CO2 is smaller than water, which may develop density flow in the deep strata or water-rock interactions in pre-existing structures, and cause the variation in permeability and pressure to induce a seismic activity. In this paper, we reviewed the mechanism of underground fluid injection induced seismicity with the focus of CCS, combined with fluid injection projects and seismic monitoring analysis in both commercial scale and experimental scale, to investigate its impact on the integrity of the cap rock of the reservoir. Finally, we summarized the appropriate site selection, injection methods and monitoring programs to prevent the occurrence of induced seismicity.
The mechanisms of intermediatedepth earthquakes were always attracting extensive researches of interest. Among various hypotheses about the mechanisms, the close relationship between the dehydration embrittlement and earthquakes is generally accepted. The intermediate-depth earthquakes in subducting slabs occur mainly in two distinct layers, corresponding with the dehydration respectively in the hydrous meta-basalts and the serpentinite layers. In the past decades, theory researches, interpretations of seismic data and laboratory experiments have been widely adopted as the major approaches to attest the hypothesis of dehydration embrittlement. However, in the latest ten years, pseudotachylytes and some brittle structures have been discovered in paleo-subduction zones like Alps, shedding a light for a new way to study intermediate-depth earthquakes.
Integrated Ocean Drilling Program (IODP) expedition 344 was implemented from October 23 to December 11, 2012 in the offshore Costa Rica, which is known for the frequent occurrence of earthquakes. This expedition is part of the Costa Rica Seismogenesis Program (CRISP) that has an overarching goal of elucidating the origin, nucleation, and propagation of earthquakes in an erosive convergent margin. We participated in this expedition. Here we present numerous aspects of this expedition in this paper including tectonic settings of the drilling area, major scientific goals, field operation, preliminary results of this expedition, and post-cruise activities. More detailed and much in-depth research is carried out after the cruise and post cruise results will be reported in the meeting to be held in Nanjing University in 2014. The synthesis of these new results should lead to better understanding of the seismogenesis of the study area.
The gas geochemical anomalies caused by underground gas releasing during some large earthquakes can be observed using high-resolution satellite remote sensing technology. Monthly CO total column and O3 total columns background field were obtained using AIRS standard product data in recent nine years (2003—2011) and earthquake cases study were conducted by the method of making differences. The temporal and spacial variations of CO and O3 distributions were summarized through analyzing the earthquakes with the magnitude more than 7 all around the world since 2003.
The variation characteristics of outgoing longwave radiation (OLR) around the time of New Zealand Earthquake M7.1 September 3, 2010 have been analyzed based on eleven years (20012011) background data using vorticity background method. The results indicated that the maximum increase of OLR was found in the month of the main shock and the position of the variation was distributed in the southwest of the epicenter. This variation was the most remarkable during the annual monthly data and monthly data in September from 2001 to 2011, which can be considered as the reflection to this earthquake. Six earthquakes with the magnitude greater than 7.0 in this region from 2001 to 2011 have been analyzed using the same method. The results have shown that OLR anomalies have been detected in three continental earthquakes and without anomalies in three coastal earthquakes. For comparison, the published reports related to OLR seismic studies have been retrieved. Only two coastal earthquakes (M8.7 off the west coast of northern Sumatra earthquake of December 2004 and M7.0 Haiti earthquake of January 2010) have been detected with OLR anomalies. According to the global distribution of cloud amount, the two regions of Sumatra and Haiti earthquakes are covered by the minimum cloud amount in global ocean. But the region of Zealand earthquake is covered by the maximum cloud amount in global ocean. So, it is believed that OLR is more sensitive to continental earthquakes than coastal earthquakes in reflecting seismic thermal infrared anomalies because water vapor and cloud can absorb much of surface outgoing infrared radiation.
A deep seismic sounding experiment was carried out for the first time in the Bohai Sea using large volume air-gun array and Ocean Bottom Seismometers (OBSs). Fifty-one OBSs were deployed along a NWW-SEE line perpendicular to the strikes of the regional tectonics and fifty were recovered successfully. Experiment outcome showed the air-gun array used during the experiment had enough power; primary data analysis indicated the OBSs recorded rich seismic phases including Ps, Pg, PmP and Pn. Initial first arrival tomography results show that the shallow layer with depth of less than 9 km has obvious heterogeneity in the lateral direction, the depth of the Cenozoic sedimentary basement is 5~6 km in the Bozhong area and the corresponding crystalline basement depth is about 9 km, and an U-shaped lower velocity body which has the trend to cut through the lower layer can be found in the Tanlu fault zone. This experiment is a successful case of the deep structure exploration in the Bohai Sea. It not only fills in the blanks of deep seismic sounding database, but also supplies fundamental information for the research of deep crustal structure around Bohai area and the development of Bohai Bay Basin.
Spectral decomposition is a more efficient method to identify reservoir than seismic attribute. It transforms the time domain of the seismic data in a certain time windows into the frequency domain by Discrete Fourier Transform. The reservoir thickness changes and boundary can be identified and imaged by the new amplitude spectrum and phase spectrum. The DFT computes an amplitude value at every hertz from the beginning frequency to the ending frequency，it has a highly deserved reputation for being safe and reliable .The fluvial sand body of Guantao formation in the Laohekou Oilfield is characteristic of thin thickness and severe variety in lateral direction. The thickness and geologic discontinuity and distribution of the sand body are predicted by the method of spectral decomposition. The results coincide well with actual drilling data.
