Surface-wave group-delay and attenuation kernels

We derive both 3-D and 2-D Fréchet sensitivity kernels for surface-wave group-delay and anelastic attenuation measurements. A finite-frequency group-delay exhibits 2-D off-ray sensitivity either to the local phase-velocity perturbation  δ c / c   or to its dispersion  ω(∂/∂ω)(δ c / c )  as well as to the local group-velocity perturbation  δ C / C   . This dual dependence makes the ray-theoretical inversion of measured group delays for 2-D maps of  δ C / C   a dubious procedure, unless the lateral variations in group velocity are extremely smooth.     

Dependence of earthquake recurrence times and independence of magnitudes on seismicity history

The fulfillment of a scaling law for earthquake recurrence–time distributions is a clear indication of the importance of correlations in the structure of seismicity. In order to characterize these correlations we measure conditional recurrence–time and magnitude distributions for worldwide seismicity as well as for Southern California during stationary periods. Disregarding the spatial structure, we conclude that the relevant correlations in seismicity are those of the recurrence time with previous recurrence times and magnitudes; in the latter case, the conditional distribution verifies a scaling relation depending on the difference between the magnitudes of the two events defining the recurrence time. In contrast, with our present resolution, magnitude seems to be independent on the history contained in the seismic catalogs (except perhaps for Southern California for very short time scales, less than about 30 min for the magnitude ranges analyzed).     

开发地震技术在扶余油层分支水平井地质设计中的应用

大庆外围东部油田开发的目的层主要为葡萄花油层和扶余油层,其中扶余油层因储层发育差,具有低孔、低渗、低丰度的特点,其未动用储量的有效开发一直是困扰油田开发的难题之一。要应用开发地震技术,结合钻井、测井、试油、沉积相等资料,通过细致描绘肇州油田芳483区块扶余油层的构造特征,预测扶余油层内部单砂体的分布形态、厚度和展布范围,为扶余油层分支水平井设计提供地质依据,同时也为有效开发扶余油层探索了新的思路。     

地震预警技术研究中的参考文献

针对潜在破坏性大地震的早期预警系统已在几个发达国家或地区运行多年,并已积累了很多成功的经验。本文收集整理了国内外有关地震预警系统研究的参考文献,以供相关领域研究者参考之用。     

1996年顺义地震的背景及其含义

针对１９９６年１２月１６日北京顺义４级地震发生的地震活动背景及其主要地震学前兆进行了研究。从地震预报角度,对北京地区中等有感地震发生前后的城地对策做了探讨。     

Is there a first-order discontinuity in the lowermost mantle?

In 1983, Lay and Helmberger [Geophys. J. R. Astron. Soc. 75 (1983) 799–837] reported the detection of a precursor to the seismic phase ScS. They attributed this precursor to a sharp seismic discontinuity located several hundred kilometers above the core–mantle boundary. Such a lowermost mantle discontinuity implies the existence of a sharp phase change or a chemical boundary. Precursors to ScS and, less frequently, PcP have since been observed in numerous locations, but are not a global phenomenon. Frequently, PcP precursors are weak or absent when ScS precursors are observed in the same location, and vice versa. There can be significant variations in the amplitude and arrival time of the precursor relative to the main phase. The presence or absence of these precursors has led to speculations about the nature of the lowermost mantle. Here we demonstrate that ScS or PcP precursors may be produced by gradients in seismic wave speed associated with large-scale lowermost mantle heterogeneity. Rather than a phase or chemical boundary with substantial topography, such gradients require lateral variations in temperature and, close to the core–mantle boundary, composition.     

Source study and tectonic implications of the 1995 Ventimiglia (border of Italy and France) earthquake (ML=4.7)

We analyse the source process and the aftershock distribution of the April 21, 1995, Ventimiglia, M_L=4.7 earthquake using the records of permanent high dynamic broad-band seismic stations and a temporary network deployed on land and at sea few hours after the earthquake. This event occurred on the western Mediterranean coast, near the border between Italy and France, at a depth of 9 km, at a point where Alpine tectonic units and Late Oligocene extensional structure overlap and are currently undergoing compressional stress. The focal solutions of the mainshock and three aftershocks depict a dominant reverse faulting with an important strike-slip component, which underlines two nodal planes: a NW–SE-dipping north fault and a NE–SW-dipping south fault. We operate a careful re-location of the aftershocks using a master-event technique and data from the temporal network and obtain a predominant NW–SE alignment. Then, we analyse the rupture process using an empirical Green function approach. We find that the mainshock broke a 0.5 to 1 km fault length and that the rupture propagated during 0.1–0.2 s probably in a SE direction. Those two arguments, together with the recent fault trace that exists close to the epicentre, leads us to propose that this event expresses the reactivation of an old transverse NW–SE structure with a dextral movement. This study thus emphasizes the role of inherited, deep-rooted, transcurrent features in the tectonic reactivation of this passive margin. It also underlines the importance of combining short-period and broad-band seismology to better resolve and understand regional tectonic processes in areas of moderate seismic activity and complex geology.