Three‐dimensional seismic tomography from P wave and S wave microearthquake travel times and rock physics characterization of the Campi Flegrei Caldera
Three‐dimensional seismic tomography from P wave and S wave microearthquake travel times and rock physics characterization of the Campi Flegrei Caldera
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Campi Flegrei Caldera 的 P 波和 S 波微地震走时三维地震层析成像和岩石物理表征
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发表时间：
2005
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通讯作者：
G. Russo
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作者：
T. Vanorio;J. Virieux;P. Capuano;G. Russo
[1]Campi Flegrei（CF）Caldera经历了世界上任何地方都无法比拟的剧烈地面变形。造成这一现象的根源仍在争论之中。为了探索破火山口的结构以及热液流体对速度变化的作用，采用了一种多学科方法，处理三维延迟时间层析成像和岩石物理特性。选定的地震数据进行了建模，使用层析成像方法的基础上，一个精确的有限差分走时计算，同时反演P波和S波初至时间的速度模型参数和震源位置。通过对CF样品岩石物理性质的实验测量，考虑到蒸汽/水相变机制影响P波和S波速度，反演的P波和S波速度图像以及推导的Vp/Vs图像进行了解释。此外，现场相关岩石的岩石物理性质的建模限制了超压流体对速度的作用。在波佐利城地下4km处存在一个平坦而低的Vp/Vs异常。地震发生在这个异常的顶部。这种异常意味着存在断裂的超压含气地层，排除了熔融岩石的存在。在浅层，位于1公里处的高Vp/Vs异常表明存在含有液相流体的岩石。最后，Vp * Vs乘积图显示出位于2 km深度处的高Vp * Vs马蹄形异常。它与重力数据和钻井数据相一致，可能构成火山口边缘的陆地剩余部分，这是使用主动源地震数据通过断层扫描在海平面以下检测到的。
[1] The Campi Flegrei (CF) Caldera experiences dramatic ground deformations unsurpassed anywhere in the world. The source responsible for this phenomenon is still debated. With the aim of exploring the structure of the caldera as well as the role of hydrothermal fluids on velocity changes, a multidisciplinary approach dealing with three-dimensional delay time tomography and rock physics characterization has been followed. Selected seismic data were modeled by using a tomographic method based on an accurate finite difference travel time computation which simultaneously inverts P wave and S wave first-arrival times for both velocity model parameters and hypocenter locations. The retrieved P wave and S wave velocity images as well as the deduced V p /V s images were interpreted by using experimental measurements of rock physical properties on CF samples to take into account steam/water phase transition mechanisms affecting P wave and S wave velocities. Also, modeling of petrophysical properties for site-relevant rocks constrains the role of overpressured fluids on velocity. A flat and low V p /V s anomaly lies at 4 km depth under the city of Pozzuoli. Earthquakes are located at the top of this anomaly. This anomaly implies the presence of fractured overpressured gas-bearing formations and excludes the presence of melted rocks. At shallow depth, a high V p /V s anomaly located at 1 km suggests the presence of rocks containing fluids in the liquid phase. Finally, maps of the V p *V s product show a high V p * V s horseshoe-shaped anomaly located at 2 km depth. It is consistent with gravity data and well data and might constitute the on-land remainder of the caldera rim, detected below sea level by tomography using active source seismic data.