Traveltime measurements from noise correlation: stability and detection of instrumental time-shifts   总被引：1，自引：0，他引：1  

L. Stehly  M. Campillo  N. M. Shapiro 《Geophysical Journal International》2007,171(1):223-230

We test the feasibility of using Green's functions extracted from records of ambient seismic noise to monitor temporal changes in the Earth crust properties by repeated measurements at regional distances. We use about 11 yr of continuous recordings to extract surface waves between three pairs of stations in California. The correlations are computed in a moving 1-month window and we analyse the temporal evolution of measured interstation traveltimes. The comparison of the arrival times in the positive and negative correlation time of Rayleigh and Love waves allows us to separate time-shifts associated with any form of physical change in the medium, those resulting from clock drift or other instrumental errors, and those due to change in the localization of the noise sources. This separation is based on the principle of time symmetry. When possible, we perform our analysis in two different period bands: 5–10 and 10–20 s. The results indicate that significant instrumental time errors (0.5 s) are present in the data. These time-shifts can be measured and tested by closure relation and finally corrected independently of any velocity model. The traveltime series show a periodic oscillation that we interpret as the signature of the seasonal variation of the region of origin of the seismic noise. Between 1999 and 2005, the final arrival time fluctuations have a variance of the order of 0.01 s. This allows us to measure interstation traveltimes with errors smaller than 0.3 per cent of the interstation traveltime and smaller than 1 per cent of the used wave period. This level of accuracy was not sufficient to detect clear physical variation of crustal velocity during the considered 11 yr between the three stations in California. Such changes may be more easily detectable when considering pairs of stations more closely located to each other and in the vicinity of tectonically active faults or volcanoes.  相似文献   

High-resolution structures of the Landers fault zone inferred from aftershock waveform data   总被引：2，自引：0，他引：2  

Hongyi Li  Lupei Zhu  Hongfeng Yang 《Geophysical Journal International》2007,171(3):1295-1307

High-frequency body waves recorded by a temporary seismic array across the surface rupture trace of the 1992 Landers, California, earthquake were used to determine fault-zone structures down to the seismogenic depth. We first developed a technique to use generalized ray theory to compute synthetic seismograms for arbitrarily oriented tabular low-velocity fault-zone models. We then generated synthetic waveform record sections of a linear array across a vertical fault zone. They show that both arrival times and waveforms of P and S waves vary systematically across the fault due to transmissions and reflections from boundaries of the low-velocity fault zone. The waveform characteristics and arrival-time patterns in the record sections allow us to locate the boundaries of the fault zone and to determine its P - and S -wave velocities independently as well as its depth extent. Therefore, the trade-off between the fault-zone width and velocities can be avoided. Applying the method to the Landers waveform data reveals a low-velocity zone with a width of 270–360 m and a 35–60 per cent reduction in P and S velocities relative to the host rock. The analysis suggests that the low-velocity zone extends to a depth of ∼7 km. The western boundary of the low-velocity zone coincides with the observed main surface rupture trace.  相似文献   

Whole mantle SH velocity model constrained by waveform inversion based on three-dimensional Born kernels   总被引：1，自引：0，他引：1  

Nozomu Takeuchi 《Geophysical Journal International》2007,169(3):1153-1163

A whole mantle SH velocity model is obtained by using a unique data set and techniques. Body and surface waveforms including major and multi-orbit phases are used as a data set and are inverted by using 3-D Born kernels. The resultant model, SH18CE, reveals the different natures of the two major upwelling systems: the strong low velocity anomalies beneath Africa extend for more than 1000 km from the core–mantle boundary (CMB), whereas those beneath the Pacific are restricted to 300–400 km from the CMB. The results also show the variable natures of stagnant slabs on the 670 discontinuity around Japan: the depths of the strongest high velocity anomalies within the stagnant slabs are different region by region, which is consistent with the detailed delay time tomography model in this area.  相似文献   

Emplacement, growth, and gravitational deformation of serpentinite seamounts on the Mariana forearc     

A. J. Oakley  B. Taylor  P. Fryer  G. F. Moore  A. M. Goodliffe  J. K. Morgan 《Geophysical Journal International》2007,170(2):615-634

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Combining InSAR and seismology to study the 2003 Siberian Altai earthquakes—dextral strike-slip and anticlockwise rotations in the northern India–Eurasia collision zone     

Edwin Nissen  Brian Emmerson  Gareth J. Funning  Anatoly Mistrukov  Barry Parsons  David P. Robinson  Eugene Rogozhin  Tim J. Wright † 《Geophysical Journal International》2007,169(1):216-232

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Expected loss‐based alarm threshold set for earthquake early warning systems     

Iunio Iervolino  Massimiliano Giorgio  Gaetano Manfredi 《地震工程与结构动力学》2007,36(9):1151-1168

Earthquake early warning systems (EEWS) seem to have potential as tools for real‐time seismic risk management and mitigation. In fact, although the evacuation of buildings requires warning time not available in many urbanized areas threatened by seismic hazard, they may still be used for the real‐time protection of critical facilities using automatic systems in order to reduce the losses subsequent to a catastrophic event. This is possible due to the real‐time seismology, which consists of methods and procedures for the rapid estimation of earthquake features, as magnitude and location, based on measurements made on the first seconds of the P‐waves. An earthquake engineering application of earthquake early warning (EEW) may be intended as a system able to issue the alarm, if some recorded parameter exceeds a given threshold, to activate risk mitigation actions before the quake strikes at a site of interest. Feasibility analysis and design of such EEWS require the assessment of the expected loss reduction due to the security action and set of the alarm threshold. In this paper a procedure to carry out these tasks in the performance‐based earthquake engineering probabilistic framework is proposed. A merely illustrative example refers to a simple structure assumed to be a classroom. Structural damage and non‐structural collapses are considered; the security action is to shelter occupants below the desks. The cost due to a false alarm is assumed to be related to the interruption of didactic activities. Results show how the comparison of the expected losses, for the alarm‐issuance and non‐issuance cases, allows setting the alarm threshold on a quantitative and consistent basis, and how it may be a tool for the design of engineering applications of EEW. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

"数字地球"与实时地震学     

许力生 《国际地震动态》2001,(8):32-37

“数字地球”是对真实地球及其相关现象的统一性的数字化重现和认识，是信息化的地球，是地球的虚拟对照体。“数字地球”的科学体系由基础研究、技术支撑和科学工程三部分组成。现代地震学同样需要基础研究、支撑技术和科学工程，其中，最后一个体系即相当于实时地震学。实时地震学调基础研究和现代技术的结合，强调地震学研究成果的转化和对社会与公众的服务，是地震学发展的“最高境界”。实时地震学需要基础研究和现代技术，更需要建立地震速报系统、地震趋势分析系统、灾害评估系统和地震救灾系统这样的系统工程。  相似文献   

Scattering behaviour at Merapi volcano (Java) revealed from an active seismic experiment     

Ulrich Wegler  Birger&#;G. Lühr 《Geophysical Journal International》2001,145(3):579-592

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Is Iceland underlain by a plume in the lower mantle? Seismology and helium isotopes     

G. R. Foulger  D. G. Pearson 《Geophysical Journal International》2001,145(3):F1-F5

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The level of deterrence provided by data from the SPITS seismometer array to possible violations of the Comprehensive Test Ban in the Novaya Zemlya region   总被引：1，自引：0，他引：1  

David Bowers  Peter D. Marshall  Alan Douglas 《Geophysical Journal International》2001,146(2):425-438

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