成都地震台网对印度洋特大地震面波震级的复测--面波震级都会饱和吗

对于2004年12月26日印度洋大地震，成都地震遥测台网有宽频带数字地震记录波形没有出格，测定的面波震级为9．0。这对于通常人们认为面波震级超过8．6可能出现饱和是一个值得注意和研究的现象。     

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

Introduction The unexpected December 26, 2004, off the west coast of northern Sumatra, Indonesia, MW=9.0 earthquake, which caused devastating tsunami around the Indian Ocean, reminds seis-mologists of the difficulty of earthquake forecast and/or prediction. For seismologists this earth-quake is almost completely unexpected, because there was neither forecasting (which means the estimation of the future earthquake rate as a function of location, time, and magnitude) nor predic-tion (forecasti…     

The rotational and gravitational signature of the December 26, 2004 Sumatran earthquake

Besides generating seismic waves, which eventually dissipate, an earthquake also generates a static displacement field everywhere within the Earth. This global displacement field rearranges the Earth’s mass thereby causing the Earth’s rotation and gravitational field to change. The size of this change depends upon the magnitude, focal mechanism, and location of the earthquake. The Sumatran earthquake of December 26, 2004 is the largest earthquake to have occurred since the 1960 Chilean earthquake. Using a spherical, layered Earth model, the coseismic effect of the Sumatran earthquake upon the Earth’s length-of-day, polar motion, and low-degree harmonic coefficients of the gravitational field are computed. Using a model of the earthquake source that is composed of five subevents having a total moment-magnitude M _w of 9.3, it is found that this earthquake should have caused the length-of-day to decrease by 6.8 microseconds, the position of the Earth’s generalized figure axis to shift 2.32 milliarcseconds towards 127° E longitude, the Earth’s oblateness J ₂ to decrease by 2.37 × 10⁻¹¹ and the Earth’s pear-shapedness J ₃ to decrease by 0.63 × 10⁻¹¹. The predicted change in the length-of-day, position of the generalized figure axis, and J ₃ are probably not detectable by current measurement systems. But the predicted change in oblateness is perhaps detectable if other effects, such as those of the atmosphere, oceans, and continental water storage, can be adequately removed from the observations.     

Integral source characteristics of the Sumatra earthquakes of December 26, 2004, and March 28, 2005

The integral characteristics of source geometry, source duration, and rupture propagation for the Sumatra-Andaman earthquake of December 26, 2004 and for the March 28, 2005 earthquake near northern Sumatra have been determined. The source parameters were found by analyzing records of the higher orbits of long-period surface waves. The results are compared with the large-scale average characteristics of tomographic models for the source process based on different data sets that diverge in some details, as well as with the aftershock distribution for the considered earthquakes.     

印尼苏门答腊西8.7级地震的几个特点及由其引发的一些思考

分析总结了印尼苏门答腊西8．7级地震的几个特点：(1)板缘特大地震;(2)引发海啸,受灾范围特别大,成灾的瞬间突发性却不如内陆地震明显;(3)在远处出现“湖面波动”等同震现象突出;(4)震前全球地震活动出现异常图像;(5)安达曼弧一带与川滇地区强震活动存在相关性。并由此提出了：尽快加紧地震海啸预警机制研究及其技术系统的建立;加强地震预测预警机制研究;要重点研究川滇地区的地震危险性;强化防震减灾科普宣传等建议。     

2004年苏门答腊大地震激发的T-波

T-波是由海底地震或者海陆边界俯冲带附近地震激发,并在海洋低速层中传播的声波.2004年12月26日,在印度洋东部印尼苏门答腊岛附近发生MW=9.3级大地震,其产生的能量在印度洋中激发了巨大的海啸,造成了严重的人员伤亡和财产损失,受到了世界科学家们极大的关注.本文从台站(PALK)及台站(DGAR)记录到的地震的信号中,提取出了清晰的高频T-波,并在频率域内分析,最终得到了T-波的频谱已及频率随时间变化图像.另外,通过对大地震时间域和频率域内T-波信号的分析,了解到此次大地震断层破裂过程持续的时间大致为500 s,其间伴随有两次明显的能量释放过程.分析数据表明两次能量释放过程的间隔大致为80~100 s.T-波分析将为推断海洋地震以及海陆边界俯冲带附近地震的特征,提供一种独立的研究手段和方法.     

Hydroacoustic contributions to understanding the December 26th 2004 great Sumatra–Andaman Earthquake

Within the era of modern digital-recording, the December 26th 2004 Sumatra–Andaman Earthquake represents an event of unprecedented scale. Hydroacoustic observations have made significant contributions toward our understanding of this great rupture and serve to reiterate the potential use of tertiary (T) waves as a tool in tsunami warning. Small-aperture arrays of hydrophones operated by the International Monitoring System (IMS) recorded the seismically generated, water-borne T-wave within the Indian Ocean. Due to the velocity structure of the oceanic water column, T-wave propagation is both slower and more efficient than radiation within the solid earth. This results in a relatively large amplitude signal that arrives within a time window distinct from the more complex and overlapping pattern of solid earth seismic phases. Hydroacoustic analysis has constrained the rupture length of the fault to be ~1,200 km and the duration on the order of 8 min, with 2–3 phases exhibiting progressively decreasing rupture velocity. These data also indicate that aftershock rates in the first hours following the mainshock correlate with spatial variability in the sourced T-wave amplitude, with far fewer events along the northern section of the main rupture. Although IMS stations telemeter data in near real time, data access for scientists was restricted due to the provisions of the Comprehensive Test Ban Treaty. The swift dissemination of data will be critical in using hydroacoustic methods to assess the magnitude and tsunamigenic potential of future events.     

2004年12月26日印度尼西亚MW9.0大震前后震源机制一致性变化特征研究

本文选取2004年12月26日发生在印度尼西亚西北近海、震中位于巽他海沟的东侧的M_W9.0地震的余震分布空间范围为研究区域,分析了该区域震源机制,并利用震源机制和构造应力场的一致性参数a进行了地震检验。研究结果表明,M_W≥7.5地震之前,都有参数a降低的现象,M_W9.0地震前,a值都有动荡起伏的情况。该研究区长达数千千米,而连续发生的M_W≥5.0地震的震源机制与构造应力场一致,应当不是随机现象,似可视为具某种前兆意义的现象。     

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, M _W=9.0 earthquake was investigated using the Harvard CMT catalogue. It is observed that before this great earthquake, 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 M _W=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. Foundation item: Ministry of Science and Technology Project (2004CB418406). Contribution No. 05FE3010, Institute of Geophysics, China Earthquake Administration.     

印尼苏门答腊MW9.0级地震对全球及中国大陆地震趋势影响研究的反思

本文对2004年12月26日印尼苏门答腊以西发生MW9.0级地震后所做的地震趋势预测做了反思,指出:关于全球特大地震近年可能连发,特大地震对几年内世界7级以上地震年频度没有明显影响,但未来几年内7级以上强震可能集中在这次特大地震附近或相关构造上的预测意见是正确的;而有关近年中国大陆及川滇地区可能发生7级强震的预测是错误的;并认为,2001年昆仑山口西8.1级地震释放了已积累的应变可能是这次特大地震不能触发中国大陆及川滇地区发生强震的重要原因。     

The wave-like structures of ionospheric perturbation associated with Sumatra earthquake of 26 December 2004, as revealed from VLF observation in Japan of NWC signals

The observations of subionospheric VLF waves from the Australian VLF transmitter NWC (frequency=19.8 kHz) at the Japanese receiving stations Chofu, Chiba and Kochi have been utilized to identify a possible precursor of ionospheric perturbations to the huge Sumatra earthquake of 26 December 2004. The VLF amplitude data at Japanese stations have indicated the depression in amplitude and also the enhancement in nighttime amplitude fluctuation before the earthquake. The nighttime fluctuation is composed of wave-like structures, and the wavelet analysis and cross-correlation analyses have been performed for those fluctuations. A significant enhancement in the fluctuation spectra in the period 20–30 min to ∼100 min (the frequency range of atmospheric gravity waves) is observed only before the earthquake. Then, the wave-like structures tend to propagate from the NWC–Kochi path to NWC–Chiba path with the time delay of ∼2 h, and so the wave propagation speed is estimated as ∼20 m/s. This finding might be important when we think of lithosphere–ionosphere coupling mechanism.     

The Sumatra tsunami of 26 December 2004 as observed in the North Pacific and North Atlantic oceans

The M _w=9.3 megathrust earthquake of December 26, 2004 off the coast of Sumatra in the Indian Ocean generated a catastrophic tsunami that caused widespread damage in coastal areas and left more than 226,000 people dead or missing. The Sumatra tsunami was accurately recorded by a large number of tide gauges throughout the world's oceans. This paper examines the amplitudes, frequencies and wave train structure of tsunami waves recorded by tide gauges located more than 20,000 km from the source area along the Pacific and Atlantic coasts of North America.     

苏门答腊Ms8.7级大震前的地脉动预警信息

介绍了辽宁数字台网运行的脉动异常跟踪系统(RTTS),叙述了这个系统在2004年12月26日08时58分55.2秒印尼苏门答腊西北近海(北纬3.9,东经95.9)8.7级地震前,营口、锦州台地脉动波形的幅度和周期明显异常的情况。并展现了利用RTTS系统进行地脉动研究的前景。     

The sumatra earthquake of December 26, 2004, as an event unrelated to the plate-tectonic process in the lithosphere

The Sumatra (Indonesia) earthquake of December 26, 2004 (M _w = 9.0?9.3), is among the strongest seismic events (occupying the second to fourth place) recorded in the epoch of instrumental seismological observations. In addition, this earthquake appears to be the first event of such a scale for which results of up-to-date high-precision geodetic measurements are available. Therefore, it is of particular interest for studies of geodynamics of mobile belts, seismogenic zones, and the Earth’s crust as a whole. The available geological, geophysical, and geodetic data for the Mediterranean-Caucasian segment of the Alpine-Himalayan mobile belt, the Greater Caucasus, and the Tajik depression suggest that the tectonic structure, geological zonality, seismicity, and present-day geodynamics of these structural elements of the Earth’s crust are controlled by the interaction of two different mechanisms of tectogenesis. First, this is the mechanism of independent self-development of the aforementioned structural elements and, first of all, the mobile belt as a whole; this mechanism acts through an intense increase in the volume and area of laminated rocks of the crust/lithosphere, apparently, due to the influx of additional mineral material supplied by an ascending flow of deep fluids. The second type of mechanisms is related to the external plate-tectonic action on the mobile belt and the other structural elements due to lateral movements of lithospheric plates. The joint analysis of geological, geodetic (GPS), and seismological data on the Sumatra earthquake area shows that these two mechanisms also act in the Indonesian part of the Alpine-Himalayan mobile belt. However, the Sumatra earthquake itself is a result of an independent (unrelated to plate tectonics) process in the mobile belt rather than the convergence of adjacent lithospheric plates.     

用10分钟P波窗估算2004年12月26日苏门答腊—安达曼地震的辐射能量

苏门答腊—安达曼MW9.1级地震的破裂过程持续了大约500秒,这一时间几乎是一般情况下用于计算远震辐射能量的P到时和PP到时之间时间窗长度的两倍。为了测量整个地震所辐射的P波,我们将时间窗扩展为从P波到时到S波到时,并用扩展窗对震中距大于60°的台站的地震记录进行分析。这些持续时间8～10分钟的窗内包含了PP,PPP,ScP震相和其他一些多次反射震相。为了测量包含这些附加震相的影响,我们计算了由扩展窗(P波到时和S波到时之间)得到的震源谱和由标准窗(P波到时和PP波到时之间)得到的震源谱的比值。对扩展窗的分析是在假设它只包含P-pP-sP波群的情况下进行的。我们分析了发生在MW9.1级主震附近具有相似深度和震源机制的4个相对较小的地震事件。这些地震的震级范围从2005年1月9日的MW6.0级余震到震中位于苏门答腊-安达曼地震南部的2005年3月28日MW8.6级的尼亚斯地震。将得到的这4个地震事件的震源谱比值取平均,就得到扩展窗的频变算子。然后对扩展窗得到的2004年12月26日主震的震源谱进行校正,就得到苏门答腊-安达曼地震整个破裂过程(～600秒)的完整的或校正的震源谱。我们计算的地震辐射总能量为1.4×1017J。经过对整个地震的校正震源谱与破裂过程的前～250秒的震源谱(由标准远震窗得到)比较,我们发现主震破裂过程的前半部分辐射的地震波能量多于破裂过程后半部分辐射能量,尤其对于周期从3秒到40秒的地震波,这种现象更加明显。     

2004年印尼苏门答腊MW9.0地震前地震活动增强现象及其与地球自转的关系

选取2004年12月26日印尼苏门答腊M_W9.0地震的余震分布空间范围为研究区域,该区域位于缅甸小板块中部,纬度范围为2°N~15°N.根据USGS地震目录,研究了2004年印尼苏门答腊M_W9.0地震前地震频次的时空变化,并分析了地震活动与地球自转的关系.结果显示:1)在余震区域范围内,地震频次自2000年开始出现了明显的上升趋势变化,反映了地震活动的增强过程,临近地震发生前,地震频次有一定幅度的回落;2)通过地震频次空间扫描,发现震前在震中附近区域地震活动增强显著;3)在1990~2004年的15年中,单位时间内发生的地震数在地球自转季节性变化减速时段与加速时段之比值r_da在震前出现明显的上升过程:1998年~2002年r_da缓慢上升,2002年底r_da快速上升达最高值,之后,r_da呈现下降趋势,直至苏门答腊M_W9.0地震发生;4)2000年1月~2004年11月间,在纬度1°N~7°N的空间范围内的震中附近地区, 5.5级以上地震都发生在地球自转季节性变化减速时段内;5)地震活动累积年频次相对于其长期平均值的变化量ΔN与地球自转"十年起伏"变化关系表现为地球自转减速时ΔN上升,地震活动增强,加速时ΔN下降,地震活动减弱.这些现象并非偶然,可能预示着地球自转减速与苏门答腊M_W9.0地震之间存在着某种联系,这些结果对地震孕育过程的认识和地震预测研究具有一定的价值.     

The seismic catastrophe of December 26, 2004, in the Indian Ocean as a tsunamigenic earthquake in island arc structures

An interpretation of the occurrence conditions and source parameters is proposed for the catastrophic earthquake of December 26, 2004, in the northwestern part of the Sunda island arc. The interpretation is based on the analysis of spatial distributions of aftershock epicenters and regions subjected to destructive tsunamis, seismicity manifestations in the NW part of the Sunda island arc in the past century, and locations of large tsunami sources of historical earthquakes off the Sumatra Island coast. The source parameters of the December 26, 2004, earthquake are compared with the reliably established main characteristics of sources of the largest tsunamigenic earthquakes in island arcs of the Pacific Ocean. According to the proposed interpretation, the December 26, 2004, earthquake source is a steep reverse fault striking NW and dipping toward the Indian Ocean. The source, ～450 km long, is located in front of the NW termination of Sumatra Island, in the southern part of the Nicobar Islands. Possible positions and sizes of large potential seismic sources in the NW part of the Sunda island arc are suggested.     

The response of water level in the YuZ-5 well, Kamchatka to the magnitude 9.3, Sumatra-Andaman earthquake of December 26, 2004

Forced and free oscillations of water level were recorded in the YuZ-5 well, Kamchatka due to the passage of seismic waves from the Sumatra-Andaman earthquake of December 26, 2004, M _w = 9.3, hypocentral distance 8250 km. The greatest amplitude of water level oscillations, at least 5 cm, was observed during the onset of seismic surface waves with a typical period of 20–50 s. The total duration of the forced and free water level oscillations was about ten hours. The available theoretical models that describe oscillations of water level in a well due to seismic waves and rapid injection of water were used to estimate the transmissivity of the aquifer. The values obtained exceed by at least two orders of magnitude the transmissivity derived from pumping test measurements. A hypothesis was proposed to explain the temporary increase in aquifer transmissivity during the passage of seismic waves by invoking disturbances in the structure of the crack-pore space and a sharp increase in aquifer rock permeability.     

芦山MS7.0地震前的电磁异常信号

对南北地震带18个地电场及电磁扰动观测台站进行了跟踪与研究, 2013年4月20日四川芦山M_S7.0地震前只有其中5个台站观测到了异常电磁信号. 研究表明, 地震前的这些异常信号时空分布非常不均匀. 在时间上表现出震前电磁异常信号在出现的台站上不是同步的, 且随着时间的推移有向震中方向迁移的趋势; 在空间上体现在成都以北的台站都没有记录到震前电磁异常信号, 主要出现在成都及其以南的一些台站. 芦山M_S7.0地震前地震电磁信号出现的最早时间是震前21天, 其次是震前16天; 临震时间则为震前5天、 4天和1天. 通过接地极注入地下的大电流以及以往的震例分析, 认为仙女山台是又一个比较突出的电磁信号观测的敏感点.      

文安5.1级地震前的电磁异常

文安5.1级地震前,电磁观测资料先后出现了背景、短期和短临异常。本文对这些异常进行了详细的分析和总结,通过对这些异常的深入研究,有助于我们在对电磁资料的分析中及时发现异常,进而对地震趋势做出比较准确的判断。