由GPS探测的Sumatra地震前电离层异常研究

2016年3月2日苏门答腊发生Mw7.8级地震.为了研究此次地震与电离层的耦合关系,采用欧洲定轨中心提供的Global Ionosphere Map(GIM)数据,利用滑动四分位距法探测了震中的TEC时间序列.在排除太阳与地磁活动的干扰后,结果发现在震前第8d震中地区电子含量明显降低,coco观测站也观测到TEC负异常现象.全球TEC异常分布图显示TEC异常持续约6h,最大幅度达到-6TECU.异常区域主要出现在孕震区内,最大异常区域并不垂直于震中位置,而是出现在靠近赤道异常边界的一侧,但是对应磁共轭区内并无明显TEC异常出现,这可能是Sumatra地震的电离层前兆之一.

对2004年北Sumatra地震序列两次强余震的灰色预测

应用灰色系统理论对2004年底北苏门答腊9.0级地震序列两次强余震(系指ML≥6)的发震时间进行了尝试性预测.对2004年12月29日6.3级余震时间进行灰色预测,预测出余震将于2004年12月29日9时7分35.6秒发生,事实上在2004年12月29日13时56分51秒发生了6.3级地震,两者相差不到5小时,比较吻合.对2005年1月1日7.0级余震进行灰色预测,预测出余震将于2004年12月31日20时37分24.6秒发生,比实际余震发生时间2005年1月1日14时25分47.2秒提前了将近18h,预测基本正确.

Detection and interpretation of the Earth's free oscillations excited by the great Sumatra-Andaman earthquake with GGP station data

The mode serials of the Earth’s free oscillation provide some important information on the Earth’s deep structure and superconducting gravimeters （SG） can investigate the phenomena of the Earth’s free oscillations with high accuracy. The great Sumatra-Andaman earthquake fully excited the Earth’s free oscillations and these signals were perfectly recorded by five superconducting gravimeters in the globe. After the pre-treatment and spectral analysis on the SG observation data, we obtained the experimented mode serials of the Earth’s free oscillations consisting of 147 modes with GGP station data. These observed modes were themselves some new important data for the study of the Earth’s deep structure. On the basis of the discussions on some checked inner-core-sensitive modes, we distinguished three layers from the inner core, and the boundary of the upper layer was compatible with the formerly known transition zone in the inner core based on seismic body waves and supported that there were the hemispherical variation and very lower shear velocity zone in the lower inner core.

GRACE detection of the medium-to far-field coseismic gravity changes caused by the 2004 Mw9.3 Sumatra-Andaman earthquake

Large earthquakes cause observable changes in the Earth’s gravity field, which have been detected by the Gravity Recovery and Climate Experiment (GRACE). Since most previous studies focus on the detection of near-field gravity effects, this study provides the results from the medium- to far-field gravity changes caused by the 2004 Sumatra-Andaman earthquake that are recorded within GRACE monthly solutions. Utilizing a spherical-earth dislocation model we documented that large-scale signals predominate in the global field of the coseismic gravity changes caused by the earthquake. After removing the near-field effects, the coseismic gravity changes show a negative anomaly feature with an average magnitude of -0.18×10-8 m·s-2 in the region ranging ～40° from the epicenter, which is considered as the 'medium ffield' in this study. From the GRACE data released by Center for Space Research from August 2002 to December 2008, we retrieved the large-scale gravity changes smoothed with 3 000 km Gaussian ffilter. The results show that the coseismic gravity changes detected by GRACE in the medium field have an average of (-0.20±0.06)×10-8 m·s-2, which agrees with the model prediction. The detection confirms that GRACE is sensitive to large-scale medium-field coseismic gravitational effects of mega earthquakes, and also validates the spherical-earth dislocation model in the medium field from the perspective of satellite gravimetry.

Co-seismic fault geometry and slip distribution of the 26 December 2004, giant Sumatra–Andaman earthquake constrained by GPS, coral reef, and remote sensing data

We analyze co-seismic displacement field of the 26 December 2004, giant Sumatra–Andaman earthquake derived from Global Position System observations,geological vertical measurement of coral head, and pivot line observed through remote sensing. Using the co-seismic displacement field and AK135 spherical layered Earth model, we invert co-seismic slip distribution along the seismic fault. We also search the best fault geometry model to fit the observed data. Assuming that the dip angle linearly increases in downward direction, the postfit residual variation of the inversed geometry model with dip angles linearly changing along fault strike are plotted. The geometry model with local minimum misfits is the one with dip angle linearly increasing along strike from 4.3oin top southernmost patch to 4.5oin top northernmost path and dip angle linearly increased. By using the fault shape and geodetic co-seismic data, we estimate the slip distribution on the curved fault. Our result shows that the earthquake ruptured ＊200-km width down to a depth of about 60 km.0.5–12.5 m of thrust slip is resolved with the largest slip centered around the central section of the rupture zone78N–108N in latitude. The estimated seismic moment is8.2 9 1022 N m, which is larger than estimation from the centroid moment magnitude（4.0 9 1022 N m）, and smaller than estimation from normal-mode oscillation data modeling（1.0 9 1023 N m）.

Growing correlation length of moderate-sized earthquakes prior to two great earthquakes near Sumatra Island

Seismic correlation length for moderate earthquakes prior to two great earthquakes in the northern sea area of Sumatra Island （Mw9.1 in 2004 and MsS. 6 in 2012） has been studied, using method of Single- Link-Cluster （ SLC ） analysis, and found to show a power-law growth about two years before their occurrences. No such growth was found for a magnitude 7 earthquake in the same area. This result suggests the occurrence of a physical process of critical-point characteristics in the source area before the great earthquakes.

Mechanism of the June 4, 2000 Southern Sumatra, Indonesia, earthquake

Mechanism of the June 4, 2000 southern Sumatra, Indonesia, earthquake (MS=8.0) are estimated from teleseismic body waves recorded by long period seismograph stations of the global seismic network. This solution is more reasonable than those reported by USGS, Harvard CMT and ERI of University of Tokyo. The best double-couple component of this earthquake is 1.51021 Nm, the compensated linear vector dipole component is 1.21020 Nm, and the explosion component is 5.91019 Nm. The focal mechanism is mainly left-lateral strike-slip, with a small thrust component. Nodal plane I: The strike is 199? the dip, 82? and the rake, 5? Nodal plane II: The strike is 109? the dip, 85, and the rake, 172. P axis: The azimuth is 154 and the plunge, 2; T axis: The azimuth is 64 and the plunge, 10; B axis: The azimuth is 256 and the plunge, 80. The P-waveforms recorded at different stations show prominent directivity. The directivity shows that the Nodal plane I is the fault plane, and that the earthquake ruptured unilaterally from the northeast to the southwest, nearly perpendicular to the strike of the Java trench.

The December 26, 2004, off the west coast of northern Sumatra, Indonesia, M_W=9.0, earthquake and the critical-point-like model of earthquake preparation

Long-term seismic activity prior to the December 26, 2004, off the west coast of northern Sumatra, Indonesia, MW=9.0 earthquake was investigated using the Harvard CMT catalogue. It is observed that before this great earth-quake, there exists an accelerating moment release (AMR) process with the temporal scale of a quarter century and the spatial scale of 1 500 km. Within this spatial range, the MW=9.0 event falls into the piece-wise power-law-like frequency-magnitude distribution. Therefore, in the perspective of the critical-point-like model of earthquake preparation, the failure to forecast/predict the approaching and/or the size of this earthquake is not due to the physically intrinsic unpredictability of earthquakes.

Organic Richness and Organic Matter Quality Studies of Shale Gas Reservoir in South Sumatra Basin, Indonesia

Talang Akar Formation is a proven hydrocarbon source rock in South Sumatra basin. The formation contains dominant shale at the top, with some sandstone interbeds. Whereas it contains coarse to very coarse sandstone beds at the bottom. The lower sandstone unit also contains carbonaceous shale and some coal seams. The geochemical analysis is important to identify a source rock quality in shale gas. The quality of source rock is determined by richness of the source rock and type of kerogen. 37 samples were collected from well cuttings in JML-1 and JML-2 wells. Samples we are received into the laboratories in the form of well site canned ditch cuttings, bagged ditch cuttings in various stages of preparation from wet, unwashed to dried, washed;sidewall cores, conventional cores, outcrop samples. The richness of a source rock can be defined by the content of organic carbon which is measured as total organic carbon (TOC). Based on geochemical result of analysis, quantity of shale hydrocarbon potential is indicated by the TOC value of 0.52 wt% - 6.12 wt% (fair to excellent criteria), with average of shale thickness more than 50 m. Tmax is an indication of the maturation stage of organic material and Hydrogen Index (HI) is a parameter used to explain the origin of organic material. HI versus Tmax crossplot was analysed for kerogen type determination and presence of type II/III kerogen was identified. This study concludes that the source rock contains abundant humic organic matter that was deposited in a transitional (Fluvio-deltaic) to marginal marine environment under oxic conditions.

Wave separation for the great Sumatra-Andaman earthquake with regional seismic array

We analyzed the seismic waveforms from the December 26, 2004 Sumatra-Andaman earthquake recorded at broadband seismic stations in western Europe. Previous studies involving of the beam-forming technique and high frequency analysis suggest that the earthquake ruptured with a duration of around 500 s. This very long duration makes P wave overlap with later arrivals such as PP wave, which follows P in about 200 s. Since P waves are crucial for modeling earthquake processes, we propose an iterative method to separate P and PP waveforms. The separated P waveform confirms a second large energy release around 300 s after the initial rupture. The iterative signal separation technique is particularly useful for mixed signals that are not independent and the number of recording stations far exceeds number of mixed signal sources.

Spheroidal oscillations of the Earth stimulated by the Sumatra-Andaman earthquake with CDSN data

The 0S2-0S54 spheroidal modes of Earth＇s free oscillations, triggered by the great Sumatra-Andaman earthquake of 26 December 2004 are retrieved from VHZ data recorded by seven upgraded stations of China Digital Seismograph Network （CDSN）. We compare these spheroidal modes with theoretical free oscillation spectra calculated from the Preliminary Reference Earth Model （PREM） and find a coincidence between their periods. Spectral splitting phenomenon is observed obviously in 0S2, 0S3, 0S4, 2S1 and 1S2 free oscillation modes. What is most noticeable is that the oscillation mode 2S1 is reported for the second time （the first time by Rosat et al） without any data stacking. We simulated the split singlet of 0S2 mode on seven CDSN stations based on general focal mechanism and seismic moment of the earthquake. The result shows that seismic moment of the earthquake can reach 10^23 N.m. We also find that the recording of Earth＇s free oscillations carries abundant information of source mechanism and earthquake location, which is applicable to the detailed study of source rupture parameters.

Estimation of postseismic deformation parameters from continuous GPS data in northern Sumatra after the 2004 Sumatra-Andaman earthquake

Continuous global positioning system （GPS） in northern Sumatra detected signal of the ongoing physical process of postseismic deformation after the M9.2 2004 Sumatra-Andaman earthquake. We analyze the character- istics of postseismic deformation of the 2004 earthquake based on GPS networks operated by BIG, and the others named AGNeSS, and SuGAr networks located in northern Sumatra. We use a simple analytical logarithmic and exponential function to evaluate the postseismic deforma- tion parameters of the 2004 earthquake. We find that GPS data in northern Sumatra during time periods of 2005-2012 are fit better using the logarithmic function with dog of 104.2 ± 0.1 than using the exponential function. Our result clearly indicates that other physical mechanisms of post- seismic deformation should be taken into account rather than a single physical mechanism of afterslip only.

Far-field deformations caused by the 2004 Sumatra earthquake

2004 苏门答腊地震在四川云南区域引起的理论水平排水量根据一个球形的脱臼理论被计算了，地震差错 model.The 重新适合理论排水量与在 situ.On 的 GPS 观察基本上一致的表演这个基础，我们计算了co地震的排水量，紧张，包括中国大陆和附近，严肃的变化和整个地球的大地水准面由这地震引起了。

The Characteristics of Seismic Activity Before the Devastating Earthquake with M_W9.0 Off the West Coast of Northern Sumatra

The characteristics of seismic activity in different time-spatial domain before the M_W9.0 earthquake were studied. The results are as follows:The activity of the deep earthquakes in the north boundary zone of the Australian plate had been evidently strengthened since 1994, showing an increased frequency, magnitude and depth, especially in regards to the heterogeneous distribution of the earthquake depth (namely between 500km and 689km). Meanwhile the shallow earthquakes of M≥7.0 in the Sumatra island and its vicinity had been obviously strengthened too, and formed a strengthening area with a length of about 1000 km and width 300 km. ②The time distribution of global strong earthquakes with M≥7.0 shows that the character of anomalous seismic quiescence-activity one year before the M_W9.0 earthquake and during its active period, the strong earthquakes formed a seismic belt striking in NWW direction. At the same time, there is a seismic gap formed by earthquakes of M≥5.0 in the epicenter and its neighboring region. ③Two deep earthquakes of M≥7.0 occurred in the west and in the east of the north boundary zone of the Australian plate half year ago. It is notable that one of them occurred in the Sumatra island where no deep earthquake with M≥6.0 has occurred in the past thirty years. ④The space distribution of moderate shocks occurring three days ago exhibited a NWW-strike seismic belt along the north boundary zone of the Australian plate. ⑤The activity of volcanoes distributed in the north boundary zone of the Australian plate had been strengthened in the past 4 years, especially several months before the occurrence of the M_W9.0 earthquake.

Estimates of potential new production in the Java-Sumatra upwelling system

The Java-Sumatra upwelling is one of the most important upwelling systems in the Indian Ocean, with maximum upwelling intensity in July through August. To estimate the nitrate supplied by upwelling, we developed a three-dimensional hydrodynamic model to calculate the mean vertical speed and determine the depth of upwelling. We used in-situ vertical nitrate profiles to assess nitrate concentration in the upwelled waters, and calculated the nitrate supply as the product of nitrate concentration and vertical transport obtained from the numerical model. The calculated result represents potential new production generated in the upwelling region. We found that on the event time scale (monthly) of Java-Sumatra upwelling, water brought to the surface originated from locations 100-m deep, giving a nitrate supply of 93.77×10 3mol/s and potential new production of 1.02×10 14gC/a.

Analysis on the Characteristics of the Coseismic Response of Water Levels Recorded in Three Wells in Hainan,China to the Two Sumatra-Andaman Strong Earthquakes

The characteristics of seismic water level fluctuations of the two Sumatra-Andaman strong earthquakes with magnitude 8.7 and 8.5 on December 26,2004 and March 29,2005 recorded at Jiaji well,Qionghai,Hainan were analyzed,the features of the infrequent "step" changes of well water level after the two earthquakes were also analyzed and the mechanism of the "step change" of well water level was discussed.Then the high-sample-rate digital observation data of seismically-induced water level fluctuations of the Sumatra-Andaman strong earthquakes with magnitude 8.7 and 8.5 recorded at Nanbin well,Sanya and Tanniu well,Wenchang were analyzed.The results suggest that the dominant period of the seismic well water level fluctuation in all three wells was comparatively accordant,the amplitudes of seismic water level fluctuation of the same earthquake in different wells were clearly different,the time duration of seismic water level fluctuations of different earthquakes at the same well was also clearly different.

Sumatran tiger(Panthera tigris sumatrae):A review of conservation status

The majority of wild Sumatran tigers are believed to live in 12 Tiger Conservation Landscapes covering approximately 88000 km^(2).However,the actual distribution of tigers across Sumatra has never been accurately mapped.Over the past 20 years,conservation efforts focused on the Sumatran tigers have increased,but the population continues to decline as a result of several key threats.To identify the status of the Sumatran tiger distribution across the island,an island-wide questionnaire survey comprised of 35 respondents from various backgrounds was conducted between May and June 2010.The survey found that Sumatran tigers are positively present in 27 habitat patches larger than 250 km2 and possibly present in another 2.In addition,a review on major published studies on the Sumatran tiger was conducted to identify the current conservation status of the Sumatran tiger.Collectively,these studies have identified several key factors that have contributed to the decline of Sumatran tiger populations,including:forest habitat fragmentation and loss,direct killing of tigers and their prey,and the retaliatory killing of tigers due to conflict with villagers.The present paper provides management authorities and the international community with a recent assessment and a base map of the actual distribution of Sumatran tigers as well as a general overview on the current status and possible future conservation challenges of Sumatran tiger management.

Ore-Forming Fluids Characteristics and Metallogenesis of the Anjing Hitam Pb-Zn Deposit in Northern Sumatra, Indonesia

The Anjing Hitam Pb-Zn deposit in northern Sumatra(Indonesia) is one of the largest Pb-Zn deposits in the region. The stratiform orebodies are mainly hosted in the middle member of the Carboniferous–Permian Kluet Formation of the Tapanuli Group. Mineral paragenesis and crosscutting relationships suggest a two-stage Pb-Zn mineralization:(I) sedimentary and(Ⅱ) hydrothermal mineralization. Ore-related calcite from both stages Ⅰ and Ⅱ contains mainly liquid-and gas-liquid two-phase-type fluid inclusions(FI). For stage I ore-forming fluids, FI homogenization temperatures(T_h) are 105 to 199 oC, and the salinities are 9.6 wt.% to 16.6 wt.% NaCleqiv, reflecting low temperature and medium-low salinity; whereas in stage Ⅱ, the T_h(206 to 267 oC) and salinity(19.0 wt.% to 22.5 wt.% NaCleqiv) are considerably higher. Fluid inclusion and C-O isotope characteristics suggest that the stage I ore-forming fluids were mainly derived from a mixture of seawater and magmatic fluids(probably from deep-lying plutons), whereas the stage Ⅱ ore-forming fluids were likely magmatic-derived with wall rock input. We propose that the Anjing Hitam deposit was a Carboniferous exhalative sedimentary(SEDEX) deposit overprinted by the Pleistocene vein-style magmatic-hydrothermal mineralization.