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首页> 外文期刊>Seismological research letters >Application of f k analysis and entropy to track the transition from spatially coherent to incoherent earthquake coda in long beach, California
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Application of f k analysis and entropy to track the transition from spatially coherent to incoherent earthquake coda in long beach, California

机译：应用f k分析和熵追踪加利福尼亚长滩从空间相干到非相干地震尾波的过渡

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Seismic-scattering theories describe high-frequency coda waves as a combination of waves from random scatterers superimposed on direct waves from the source. The direct waves are expected to be spatially coherent whereas the scattered waves, arriving with random phase, will be spatially incoherent. Our objective is to use data from an extreme high-resolution seismic experiment in Long Beach, California, to determine the transition from coherent to incoherent coda. The network, deployed by Nodal Seismic, comprises ～5400 vertical component instruments, spaced every ～100 m over an area of ～5 × 7 km~2. It was deployed for a period of six months with the primarily target to image the geological structure of the area for oil exploration. During the deployment, several thousand earthquakes and microearthquakes were recorded. We examine coda waves from the two largest events that occurred in the vicinity of the array.We compute frequency-wavenumber diagrams to determine the sources of coda and their evolution in time. Entropy analysis of the propagation of seismic waves through the array indicates the transition between the coherent direct body waves and the onset of incoherent coda waves. Our analysis illustrates that after the arrival of the body waves, the seismic coda is initially dominated by a dispersing wave train composed of spatially coherent body waves, forward scattered from 1D crustal layering. This is then followed by omni-directional, spatially incoherent coda waves that can be described as scattered waves from 3D random sources.
机译：地震散射理论将高频尾波描述为来自随机散射体的波的组合，叠加在来自源的直接波上。期望直接波在空间上是相干的，而以随机相位到达的散射波在空间上是不相干的。我们的目标是使用来自加利福尼亚长滩的超高分辨率地震实验的数据来确定从相干尾声到非相干尾声的过渡。该网络由Nodal Seismic部署，包括〜5400个垂直分量仪器，在〜5×7 km〜2的区域中每〜100 m间隔开。它被部署了六个月的时间，主要目标是对石油勘探区域的地质结构进行成像。在部署期间，记录了数千次地震和微地震。我们从阵列附近发生的两个最大事件中检查了尾波，并计算了频率-波数图以确定尾声的来源及其时间演变。地震波在阵列中传播的熵分析表明相干直接体波与非相干尾波开始之间的过渡。我们的分析表明，在体波到达之后，地震尾波最初由一维分散的波列控制，该波列由空间相干的体波组成，从一维地壳分层中向前散射。然后是全方向，空间不连贯的尾波，可以将其描述为来自3D随机源的散射波。

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