Ambient Near-Coastal Seismic Noise and Temporal Monitoring

研究人员将利用次级海洋微震噪声的位置来提高地壳速度变化的临时分辨率，并绘制初级海浪的海岸反射位置图。提出的微震震源定位技术是基于一种为实时地震定位而开发的算法，适用于像南加州这样的地区，那里有多个同时发生的震源位于近海几百公里以内，并且在陆地上有分布良好的地震台阵。震源位置的使用克服了标准相关方法的一个问题，即需要随机分布震源以实现精确的测量，这意味着较长的相关时间，从而降低了时间分辨率。使用一组震源位置，可以在对比中使用较短的合成地震记录。由高分辨率波作用模型(WAM)确定的入射主波场和假设的反射源形成一个伴随问题，从而确定海岸反射点。用模拟和实际资料实例说明了震源定位过程。结果表明，在任意给定条件下，往往有多个源点处于活动状态。它们提供了两种独立的方法：(1)合成孔径雷达(SAR)测量震源区的波-波相互作用强度？微震发生的必要条件。一种新的空中系统，将于2008年6月在加利福尼亚州南部近海上空飞行，以寻找指示震源点的相反海洋波场。(2)用震源位置和海洋微震理论计算的观测到的微震幅度与估计的幅度之间的比较。目前对海岸反射的性质了解很少。这项研究将提供机会，为这一过程开发一个模型，并最终产生一个完整的波场描述，可以被并入下一代波行动模型。微震提供了一种持续监测洛杉矶盆地瑞雷波速度的方法，作为应力变化的潜在指标。在这一过程中，震源的使用提高了时间分辨率，并消除了由于随机震源位置假设造成的系统偏差问题。这项研究连接了雷达干涉测量、海洋学和地震学这三个领域，因此有可能推动所有这些领域的研究。确定海岸反射的机制将大大加强社区波作用模式。南加州的应用可以扩展到其他几个地区，包括加州北部、卡斯卡迪亚和日本。这项研究建立的程序可以成为南加州标准地震监测的一部分

The researchers will use the locations of secondary ocean microseisms noise to improve thetemporal resolution of changes in crustal velocity, and to map the locations of coastalreflections of primary ocean waves. The proposed microseisms source location techniqueis based on an algorithm developed for real-time earthquake locations and is suitable forareas like Southern California where multiple simultaneous sources are located within afew hundred km offshore and where there is a well distributed seismic array on land. Theuse of source locations overcomes a problem with standard correlation methods thatrequire a random distribution of sources to achieve precise measurements, whichtranslates to long correlation times and hence a reduced temporal resolution. Using a setof source locations, a shorter synthetic seismogram can be used in the correlation. Thecoastal reflection points will be determined by forming an adjoint problem with thehypothesized reflection source and an incident primary wavefield determined from high resolutionWave Action Models (WAM's).The source locations procedure is demonstrated with both a synthetic and real dataexamples. The results show that there are often many source points active at any giventime. They provide two independent approaches: (1)Synthetic Aperture Radar (SAR) measurements of the intensity of wave-waveinteractions at the source regions ? a necessary condition for microseisms generation. Anew airborne system that will be flown in June 2008 over the offshore S. California tolook for opposing ocean wavefields which are indicative of the source points. (2) Acomparison between the amplitudes of the observed micoseisms and estimatedamplitudes calculated using the source locations and the theory of ocean microseisms.The nature of thecoastal reflections is currently poorly understood. This research will provide theopportunity to develop a model for this process and to ultimately to generate a descriptionof the complete wave-field that can be incorporated into the next generation of WaveAction Models. Microseisms provide a means to continuously monitor the Rayleighwave speed across the Los Angeles basins as a potential proxy for stress changes. Theuse of sources in this procedure increases the temporal resolutions and removes theproblem of systematic bias due to the assumption of random source locations.This research bridges three communities: radar interferometry,oceanography and seismology and hence has the potential to spur research in all theseareas. Determining the mechanisms for coastal reflections will significantly enhance thecommunity wave action models. The application to southern California can be extendedto several other areas including northern California, Cascadia, and Japan. The procedureestablished by this research could become part of the standard seismic monitoring ofSouthern California