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1.
— The unusual tsunami generated by the July 17, 1998 Papua New Guinea earthquake was investigated on the basis of various geophysical observations, including seismological data, tsunami waveform records, and on-land and submarine surveys. The tsunami source models were constructed for seismological high-angle and low-angle faults, splay fault, and submarine slumps. Far-field and near-field tsunamis computed from these models were compared with the recorded waveforms in and around Japan and the measured heights along the coast around Sissano Lagoon, respectively. In order to reproduce the far-field tsunami waveforms, small sources such as splay fault or submarine slump alone were not enough, and a seismological fault model was required. Relocated aftershock distribution and observed coastal subsidence were preferable for the low-angle fault, but the low-angle fault alone could not reproduce the large near-field tsunamis. The low-angle fault with additional source, possibly a submarine slump, is the most likely source of the 1998 tsunami, although other possibilities cannot be excluded. Computations from different source models showed that the far-field tsunami amplitudes are proportional to the displaced water volume at the source, and the comparison with the observed tsunami amplitudes indicated that the displaced water volume at the 1998 tsunami source was ～0.6 km3. The near-filed tsunami heights, on the other hand, are determined by the potential energy of displaced water, and the comparison with the observed heights showed that the potential energy was ～2 × 1012 J. 相似文献
2.
由于印度-欧亚板块碰撞,位于板块边界带的喜马拉雅地区大震频繁,但对其活动性的认识仍十分有限.2015年4月25日尼泊尔中东部地区时隔80年再次发生8级地震,为研究板缘地震提供了一次难得机遇.本文用西藏和尼泊尔的GPS连续观测数据和全球分布的远震地震波记录联合反演此次特大地震的破裂过程,结果显示此次地震发生在印度板块与青藏高原接触边界面——喜马拉雅主滑脱断层上.北倾11°、近东西(295°)走向的断层面破裂约100km长(博卡拉到加德满都),130km宽(从加德满都深入我国西藏吉隆县),破裂以逆冲滑动为主,平均幅度达到2.4m,释放的地震矩高达9.4×1020 N·m.反演结果还显示,震源体主要破裂分布深度范围为5~25km,应无地表破裂,属于一次盲地震.基于GPS资料推测的地壳现今运动速率及1833年地震的震源位置,我们推测地震在此次地震破裂区域复发的周期可能为150~200a,而极震区以南的深部滑脱断层仍保持闭锁,未来仍有导致灾害性大震的可能性. 相似文献
3.
Tomoyuki Takahashi Takeyuki Takahashi Nobuo Shuto Fumihiko Imamura Modesto Ortiz 《Pure and Applied Geophysics》1995,144(3-4):747-767
A source model for the 1993 Hokkaido Nansei-Oki tsunami must satisfy certain conditions. Such conditions are presented in this paper, and two methods are used to determine the best source model for this event. A trial-and-error method selects DCRC-17a as the best among 24 different models. This model has three fault planes dipping westward. To reproduce well the tide gauge records at two locations, an inversion analysis is used to modify the dislocation of DCRC-17a. 相似文献
4.
《Geofísica Internacional》2014,53(2):211-220
We apply a single-step, finite-fault analysis procedure to derive a coseismic slip model for the large MW 7.4 Ometepec-Pinotepa Nacional, Mexico earthquake of 20 March 2012, using teleseismic P waveforms recorded by the Global Seismographic Network. The inversion is conducted in near-realtime using source parameters available from the USGS/NEIC and the Global Centroid Moment Tensor (gCMT) project. The fault orientation and slip angle are obtained from the gCMT mechanism assuming that the fault coincides with the shallow-dipping nodal plane. The fault dimensions and maximum rise time are based on the magnitude reported for the event. Teleseismic data from the USGS/NEIC Continuous Waveform Buffer database are used in the inversion with record start times set to the P-wave arrivals used to compute the earthquake hypocenter. The inversion is stabilized by requiring a smooth transition of slip across the fault while minimizing the seismic moment. These constraints are applied using a smoothing weight that is estimated from the inverse problem, allowing the recovery of the least-complicated rupture history in a single step. Inversion of the deconvolved, ground-displacement waveforms reveals a simple, circular rupture similar in extent to the source identified by the USGS/NEIC using body-and surface-wave data, indicating that the teleseismic P waves can provide a first-order source model for the event in near-realtime. Additional inversions conducted using velocity records identify a more-detailed rupture model characterized by an elliptical 2500 km2 source region extending updip and downdip from the hypocenter. This elliptical source preserves the orientation and overall dimensions of a dual-source slip model obtained recently by other investigators using local strong motions and global seismic waveforms. The results indicate that velocity waveforms could provide additional details of the earthquake rupture in near-realtime, finite-fault inversions using teleseismic P waves. 相似文献
5.
利用地震波资料对澄江5．2级地震序列的震源机制、震源应力场和震源断层作了分析研究。结果表明，整个序列发展中，震源区及附近、构造应力场以南东东方向、水平作用为主的压应力场为主。其次还有南南东向、水平作用为主的压应力场的作用。由序列震源机制解分析，主震发震断层是走向北北东、倾角较陡的断层面，在南南东－南东向，接近水平的压应力场作用下，该断层面具有以左旋走滑为主的错动性质。该断层面是序列的主破裂面。在序列发展过程中，北西西－北西向断层也参与了活动。有的余震，虽然发生在与主破裂面一致或接近的断层面上，但破裂错动的旋性发生了变化，出现了相对主破裂事件的反向错动。极少数余震破裂错动性质呈现以倾向滑动为主的特征。在序列发展过程中，破裂面及其错动性质显地复杂。由于强震的发生，主破裂的错动，使得震源区局部应力场状态错综复杂。 相似文献
6.
A fault plane model and a finite element hydrodynamic model are applied to the simulation of the Hokkaido Nansei-Oki tsunami of July 12, 1993. The joint performance of the models is assessed based on the overall ability to reproduce observed tsunami waveforms and to preserve mass and energy during tsunami propagation. While a number of observed characteristics of the waveforms are satisfactorily reproduced (in particular, amplitudes and arrival times at tidal gauges relatively close to the source, and general patterns of energy concentration), others are only marginally so (notably, wave periods at the same gauges, and wave heights along Okushiri); differences between observations and simulations are traceable to both the fault plane and the hydrodynamic models. Nonnegligible losses of energy occur throughout the simulated tsunami propagation. These losses seem to be due to a combination of factors, including numerical damping and possible deficiencies of the shallow water equations in preserving energy. 相似文献
7.
2013年2月19日四川省绵阳市三台县发生MS4.7地震,震中位于四川盆地中部基底断裂绵阳—三台—大足断裂与蒲江—三台—巴中断裂的交会区域。基于地震目录、震相报告和波形等资料,对地震序列进行重定位,采用近远震联合波形反演求解主震震源机制,结合野外地质调查对该地震的发震构造进行分析。余震序列重定位的空间展布方向为NW-SE向,与节面Ⅰ走向吻合,认为此次地震发震断裂走向为NW?SE,倾向为NE,且破裂面近于直立,发震断层在近NS向的近水平挤压应力作用下作右旋走滑错动。实地调查中未见地表破裂及地表断层行迹,认为发震构造为一隐伏断裂。重定位及通过近远震联合反演所得震源深度分别为21.6和19 km,震源深度反映震源区位于上地壳底部的低速层内。此次地震可能是汶川地震造成的区域构造应力场改变与调整过程中,四川盆地川中地块内隐伏于前震旦纪结晶基底中的高角度断裂重新活动的结果。 相似文献
8.
At large hypocentral distances, it is convenient to approximate the curved transient seismic wavefronts as planar to estimate rotational ground motions from the single-station recordings of translational ground motions. In this paper, we investigate whether and when this approximation, referred to as the ‘plane-wave’ approximation, can be considered adequate close to the source. For this, we consider a simplistic source model comprising a two-dimensional, kinematic shear dislocation SH line-source buried in a homogenous, elastic half-space and assume this to be an equivalent representation of a finite-sized fault. The ‘plane-wave’ rotational motion is then synthesized from the exact translational motion solution to the assumed model and compared with the exact rotational motion solution for this model. The comparison between the two sets of rotational amplitudes in frequency domain suggests that the plane-wave approximation may be adequate, when the wavelengths of the seismic waves are much smaller than the source depth. When this is not true, the plane-wave approximation is seen to underestimate the Fourier amplitudes close to the source by several orders, particularly when the fault planes are vertically oriented. A similar comparison in the time domain indicates that a severe underestimation may also occur when the source rise time is longer than the shear-wave arrival time at the epicenter. Significant discrepancies are also observed between the waveforms of the exact and plane-wave rotational motions. 相似文献
9.
N-type earthquakes sometimes occur before the eruption of andesitic volcanoes, but their source mechanism has not been understood well. Their waveforms have stationary periods and decay slowly resembling to damped oscillation. They have common characteristics of spectra among the different stations; these spectral peaks appear at almost equal intervals of 1.0 Hz with common sharpness. We made detailed analysis on the N-type earthquakes observed at Asama volcano in July 1995. During 10 days activity, the duration of each earthquake increased gradually from 40 s to 3 min, while the peak frequency decreased from 2.7 to 0.8 Hz. Hypocenters are distributed slightly west under the summit crater with 0.4–1.7 km above sea-level. Source mechanism of the N-type earthquake is determined using a waveform inversion technique. Synthetic waveforms are calculated using 2D finite difference method. Surface topography is included in the calculation to incorporate the case that the source region is higher than the stations. Since the optimum solution has a large volumetric component, we approximated the volumetric part as a volume change of fluid filled sphere or cylinder or plane crack, and decomposed the solution into volumetric and non-volumetric part. Consequently, it is revealed that the optimum solution can be expressed as “crack expansion (contraction)+small fault slip”, because the spectral peak distribution advocates the crack expansion model among these three candidates. The frequency change during this activity may be explained by the time variation of the sound speed of inner fluid from 300 to 100 m/s. The change of the void fraction of water–steam phase might have caused the decrease of the sound speed. 相似文献
10.
IntroductionNowadaystheprecisionofgravitymeasurementisupto10xlo--8InjsZ(Okubo,1992),theprecisionofaltimetryisoftheorderofmm,andtheprecisionofrelativemeasurementinhorizontaldirectionusingGPStechniquesreaches(0.01--0.001)x10ed(Liu,etal,1998).Thegravitychangesinducedbyalargeearthquake(e.g.,Tangshanearthquakeof1976)canbetensorevenhundredsof10--8m/s',andthemaximumdisplacementinhorizontalandverticaldirectioncreatedbyitalwaysexceedI.0m(Chen,etal,1979,1980,Zhang,etal,1981).Therefore,structuresrela… 相似文献
11.
2009年4月6日意大利L'Aquila地区发生了Mw6.3级地震,该地震造成了300余人的人员死亡. 本文联合不同波长、不同入射倾角的升降轨Envisat和ALOS卫星的差分干涉数据对该地震进行震源机制解的反演研究. 研究首先对卫星雷达影像进行二通差分干涉处理,获取了覆盖L'Aquila地震震区的完整InSAR同震形变场,然后结合四叉树和均匀采样方法对原始观测数据进行降采样. 在此基础上,联合GPS形变观测数据,利用弹性半空间矩形和三角位错模型,以及断层自动剖分技术对断层面进行最优离散剖分,反演获取了发震断层的精确几何参数和最优断层滑动分布,结果显示分布式三角位错滑动模型能够很好地解释观测到的地表形变场. 反演结果表明发震断层是一个以正倾滑为主兼有少量右旋走滑的盲断层;基于观测数据最优确定的断层单元的最短边长为0.4 km,最长边长为6.3 km;此次地震的滑动分布主要发生在5～14 km深度的范围内,最大滑移量为1.07 m,释放的能量为3.43×1018 N·m(Mw6.32),与地震学的研究结果非常一致. 相似文献
12.
快速准确的海啸源模型是近场海啸精确预警的关键.尽管目前还没有办法直接对其进行正演定量计算,但是可以通过多源地震、海啸观测数据进行反演或联合反演推算.不同的海啸源可能导致不同的预警结论,了解不同类型海啸源适用性、评估海啸源特征差异对近场海啸的影响,无论对于海啸预警还是海啸模拟研究尤为重要.本文评估分析了6种不同同震断层模型对2011年3月11日日本东北地震海啸近场数值预报的影响,重点对比分析了有限断层模型与均一滑动场模型对近场海啸产生、传播、淹没特征的影响及各自的误差.研究表明:近场海啸波能量分布主要取决于海啸源分布特征,特别是走向角的差异对海啸能量分布影响较大;有限断层模型对海啸灾害最为严重的39°N以南沿岸地区的最大海啸爬坡高度明显优于均一滑动场模型结果;综合对比DART浮标、GPS浮标及近岸潮位站共32个站次的海啸波幅序列结果发现有限断层模型整体平均绝对/相对误差比均一滑动场模型平均误差要低,其中Fujii海啸源的平均绝对/相对误差最小,分别是0.56m和26.71%.UCSB海啸源的平均绝对/相对误差次之.3个均一滑动场模型中USGSCMT海啸源模拟精度最高.相对于深海、浅海观测站,有限断层模型比均一滑动场模型对近岸观测站计算精度更高.海啸源误差具有显著的方向性,可能与反演所采用的波形数据的代表性有关;谱分析结果表明Fujii海啸源对在12至60min主频波谱的模拟要优于UCSB海啸源.海啸源中很难真实反映海底地震破裂过程,然而通过联合反演海啸波形数据推算海啸源的方法可以快速确定海啸源,并且最大限度的降低地震破裂过程与海啸产生的不确定性带来的误差. 相似文献
13.
作为"一带一路"地震台网项目的子项目,鹤岗地震台阵区域位置特殊,在地震监测中担负着重要使命。2019年,黑龙江省地震局采用Reftek-130B地震数据采集器和CMG-3T宽频带地震计,完成台阵前期勘选工作,连续波形记录时间30天以上,波形记录质量良好。利用该台阵已勘选的15个点位连续波形记录,估计各点位功率谱,通过绘制概率密度函数图和单频曲线,初步分析该地区背景噪声变化特征。分析结果表明,各勘选点位的噪声功率谱密度相对稳定,部分点位受人类活动影响,在10 Hz以上存在突变,3-5、3-6、4-4子台高频变化较为明显,勘选点位的背景噪声变化特征可为今后的地震台阵建设提供依据。 相似文献
14.
根据形变测量资料和有关实验结果以及某些地震前兆特征,本文提出了一种在粘弹性介质半空间中断层滑动面沿断裂带走向扩展,即断层蠕动传播的力学模型.为了研究其附近的形变特征,导出了蠕动传播所产生位移场的解析表达式,并通过数值积分计算了在广义开尔文介质中,滑动时间函数为△U=B(1-e-t/T),而蠕动事件沿断裂带单侧和双侧传播导致的附近介质位移的时空分布.根据1976年唐山地震前沧东断裂带上的短周期测量资料并参考模型所得出的结果,对震前的断层运动作了反推.结果表明,地震前沿沧东断裂带发生过明显的蠕动传播,其初始蠕动发生在小站和沧州之间,随后蠕动沿着断裂带向东北和西南传播,向西南扩展的滑动面是顺扭走滑运动,向东北扩展的滑动面以顺扭走滑运动为主并略有压性倾滑运动分量. 相似文献
15.
Mihailo D. Trifunac 《地震工程与结构动力学》1973,2(1):59-69
Prediction of response spectra for earthquake engineering purposes is considered from a new point of view based on the dislocation theory of earthquakes. It is shown that the traditional scaling of response spectra by the predicted peak acceleration should be limited to the high-frequency end of the spectrum, and that the peak acceleration in the near field is not strongly correlated with earthquake magnitude. The amplitude of the long-period end of response spectrum at source to station distances greater than about 10 source dimensions should be scaled with seismic moment, while for distances less than about one source dimension this amplitude should be proportional to the permanent ground displacement. To reconcile the existing extensive data on seismicity of active regions based on magnitude scale, it is shown that magnitude can be used to determine approximately the seismic moment. 相似文献
16.
近场强地震动除受场地条件的影响外,还受到震源破裂面上子源的空间分布特点、子源破裂先后顺序的强烈控制,基于数值格林函数法的近场强地震动数值模拟方法可以综合考虑震源、传播途径及局部场地条件的影响,对计算过程进行合理简化,分2步完成地震动模拟:第1步,在介质均匀区采用矩张量的解析解计算所有子源在盖层底面的位移,形成下一步有限元计算的输入场;第2步,在盖层介质不均匀区,结合局部人工透射边界技术,采用时、空解耦的波动显式有限元方法计算地表强地震动。在有限断层模型中,采用具有9个力偶的等效地震矩张量表达断层产状、滑动方向等的影响,采用Brune模型定义各子源的滑动时间函数,描述滑动的时、空不均匀分布特征,从而细化震源模型。通过对Northridge地震中4个基岩台站地表地震动的模拟结果和强震记录,验证了此简化计算方法的可行性 相似文献
17.
高频GPS可以实时获取地表位移数据,在地震学中有十分重要的现实应用,比如快速获取震中、震级、地震烈度甚至震源破裂过程.本文以汶川地震为例,首先利用近场7个GPS台站数据反演震中位置,由于高频GPS和测震学确认的震相不一致,两种震中结果相距约15.7 km.然后对高频GPS和强震动数据进行了比较分析,我们的统计结果表明,尽管由于工作原理不同,高频GPS数据中的地震动峰值与强震记录相比存在明显差异,但是高频GPS记录的PGA、PGV和PGD同样可以作为计算地震烈度的指标.进而,使用SMBLOC程序对强震记录进行事后的基线偏移校正,得到与实时高频GPS精度相当的地表位移序列.最后,采用移动平均窗口对这些位移数据作平滑,基于最速下降法和OKADA模型,对汶川地震断层破裂的过程进行了回溯性准实时反演.结果表明,汶川地震主断层由西南向东北方向破裂,以14∶28∶04为基准,在震后20 s提供初始震级MW7.0,震后70 s震级稳定在MW7.8,但断层仍在破裂,在震后159 s根据位移波形判断事件基本结束.研究表明,实时地表位移数据可以快速准确获取强震震级和破裂方向,从而使得高频GPS将对现有地震预警系统提供很好的补充. 相似文献
18.
In order to determine how reliably one can invert accelerograms to determine the rupture process details, when the station configuration is less than optimal, we use the vertical component of synthetic accelerograms for a Haskell-type earthquake rupture model, at stations in the vicinity of a dip-slip fault and solve the inverse problem. Of the various station configurations used, one is a uniform distribution and the others are very non-uniform. Faults of two different aspect ratios are considered. We mainly use much larger spatial and temporal cell sizes in the inversion than we use to construct the artificial data. The fault mechanism and the fault area are taken as known in the inversions. To solve the inverse problem, we use the method of linear programming and stabilize the solution by the use of physical constraints. The constraints of positivity of the slip rates on the fault is used in all cases in this study. In some cases, additional physical constraints such as preassigning the final moment, the rupture speed, and so on, are also used. We find that using a cell size almost double the wavelength of interest, we are able to reproduce the solution of the problem, even when we add a small amount of random noise to the artificial data, provided the source medium structure is known. We show that the best station configuration is when the stations are on the hanging wall, due to the fact that they provide the best illumination of the fault surface. This provides an incentive to install permanent ocean bottom strong ground motion stations in subduction zones. We also analyzed the effect of the rupture propagation direction on the results of the inversion showing that even four stations are sufficient to retrieve the rupture process if they are in the forward direction of the rupture propagation; the results for this case are better than when the four stations are placed in the backward direction, even when their positions are such that they illuminate the fault in exactly the same way as the four stations in the forward direction. Thus azimuthal distribution and the resulting illumination of the fault as well as the relation of the position of the stations to the direction of rupture propagation are more important than simply the number of stations. Finally, we find that proper knowledge of source medium structure is essential to recover the source process details reliably and that poor knowledge of crustal structure cannot be compensated by adding stations or by additional constraints. 相似文献
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采用Yoshimitsu Okada及Steketee的断裂位错模型和汶川地震现有成果,通过坐标转换和合成矢量的方法将断裂位错模型用于映秀—北川断裂、灌县—安县断裂和北川—青川断裂组成的断裂系统的错动研究中,理论上计算龙门山近断裂地区的水平位移场(包括沿走向和垂直走向方向)和垂直位移场从震源到地表的分布.模型参数源于现有的研究成果和野外实地考察,计算得到的地表位移场与先前研究成果,包括GPS实测数据,具有的近似性表明了模型的正确性.但GPS只能测定地表水平和垂直变形,对于地下变形情况及其分布却无法描述;目前对于地下变形的研究主要基于对大量仪器记录的地震资料进行反演或通过野外观测进行推测;但是反演多集中于空间较大范围,这样虽可阐述断裂运动引起的大范围位移趋势,而对于震源附近空间介质位移的描述却略显粗糙;同时,野外观测误差较大.本文通过理论模型计算汶川地震中近断裂区域(距断裂50km)内的位移及分布.由计算发现在近断裂区域内垂直位移场和垂直走向方向位移场变化趋势一样,幅值都是从震源到地表逐渐减小;沿断裂走向方向的水平位移场从震源到地表逐渐变大,同时计算还表明位移场的变化在断裂上盘比下盘剧烈,余震分布主要集中于断裂上盘,这说明余震分布和位移剧烈程度存在某种相关性. 相似文献