Adjoint analysis of the source and path sensitivities of basin-guided waves
Adjoint analysis of the source and path sensitivities of basin-guided waves
复制标题
盆地导波源和路径敏感性的伴随分析
DOI：
--
复制
发表时间：
2012
期刊：
影响因子：
--
通讯作者：
Kim B. Olsen
中科院分区：
文献类型：
--
作者：
Steven M. Day;D. Roten;Kim B. Olsen
总结
对南部圣安德烈亚斯断层（SAF）地震破裂的模拟显示，圣盖博和洛杉矶盆地（SGB和LAB）明显与长程路径效应有关。在不同的SAF模拟中，可以重复识别几何上相似的激发模式（例如，Love波状能量，主要周期约为4 s，从SGB向西南方向输送到LAB），但激发这些独特波场模式的振幅会发生变化，这取决于震源的详细信息（滑移分布、破裂方向和速度）。我们描述了一种方法，用于快速计算这种预测的波场特征的源运动学扰动的灵敏度，使用时间反演（伴随）波场模拟。的计算是类似于在伴随断层扫描，和相同的时间反演计算也产生路径敏感性内核，使进一步深入了解的激励机制。对于SAF最南端300 km处的破裂，LAB激发最大的是集中在北方Coachella山谷和横向范围之间的滑移，沿该断层段向NE传播，破裂速度在3250和3500 m s-1沿着之间;也就是说，在速度范围内或略高于速度范围（瑞利和S速度之间），这是积极排除在一个尖锐的破裂前的限制，突出的潜在价值施加物理约束（如从自发破裂模型）源参数化。LAB激发是弱破裂的SW和破裂在任何一个方向位于北部的横向横向范围，而文图拉盆地（VTB）的东北断裂位于北部的横向范围优先激发。路径核表明，LAB激发介导的表面波偏转的速度对比沿着南部边缘的横向范围，有他们的大部分能量在基底岩石，直到他们的东部边缘上的SGB，通过它，然后他们进入LAB漏斗。VTB放大通过类似的波导效应增强。
SUMMARY
Simulations of earthquake rupture on the southern San Andreas Fault (SAF) reveal large amplifications in the San Gabriel and Los Angeles Basins (SGB and LAB) apparently associated with long-range path effects. Geometrically similar excitation patterns can be recognized repeatedly in different SAF simulations (e.g. Love wave-like energy with predominant period around 4 s, channelled southwestwardly from the SGB into LAB), yet the amplitudes with which these distinctive wavefield patterns are excited change, depending upon source details (slip distribution, direction and velocity of rupture). We describe a method for rapid calculation of the sensitivity of such predicted wavefield features to perturbations of the source kinematics, using a time-reversed (adjoint) wavefield simulation. The calculations are analogous to those done in adjoint tomography, and the same time-reversed calculation also yields path-sensitivity kernels that give further insight into the excitation mechanism. For rupture on the southernmost 300 km of SAF, LAB excitation is greatest for slip concentrated between the northern Coachella Valley and the transverse ranges, propagating to the NE and with rupture velocities between 3250 and 3500 m s–1 along that fault segment; that is, within or slightly above the velocity range (between Rayleigh and S velocities) that is energetically precluded in the limit of a sharp rupture front, highlighting the potential value of imposing physical constraints (such as from spontaneous rupture models) on source parametrizations. LAB excitation is weak for rupture to the SW and for ruptures in either direction located north of the transverse transverse ranges, whereas Ventura Basin (VTB) is preferentially excited by NE ruptures situated north of the transverse ranges. Path kernels show that LAB excitation is mediated by surface waves deflected by the velocity contrast along the southern margin of the transverse ranges, having most of their energy in basement rock until they impinge on the eastern edge of SGB, through which they are then funnelled into LAB. VTB amplification is enhanced by a similar waveguide effect.