SUMMARY Knowledge of attenuation structure is important for understanding subsurface material properties. We have developed a double-difference seismic attenuation (DDQ) tomography method for high-resolution imaging of 3-D attenuation structure. Our method includes two main elements, the inversion of event-pair differential ${t^*}$ ($d{t^*}$) data and 3-D attenuation tomography with the $d{t^*}$ data. We developed a new spectral ratio method that jointly inverts spectral ratio data from pairs of events observed at a common set of stations to determine the $d{t^*}$ data. The spectral ratio method cancels out instrument and site response terms, resulting in more accurate $d{t^*}$ data compared to absolute ${t^*}$ from traditional methods using individual spectra. Synthetic tests show that the inversion of $d{t^*}$ data using our spectral ratio method is robust to the choice of source model and a moderate degree of noise. We modified an existing velocity tomography code so that it can invert $d{t^*}$ data for 3-D attenuation structure. We applied the new method to The Geyser geothermal field, California, which has vapour-dominated reservoirs and a long history of water injection. A new Qp model at The Geysers is determined using P-wave data of earthquakes in 2011, using our updated earthquake locations and Vp model. By taking advantage of more accurate $d{t^*}$ data and the cancellation of model uncertainties along the common paths outside of the source region, the DDQ tomography method achieves higher resolution, especially in the earthquake source regions, compared to the standard tomography method using ${t^*}$ data. This is validated by both the real and synthetic data tests. Our Qp and Vp models show consistent variations in a normal temperature reservoir that can be explained by variations in fracturing, permeability and fluid saturation and/or steam pressure. A prominent low-Qp and Vp zone associated with very active seismicity is imaged within a high temperature reservoir at depths below 2 km. This anomalous zone is likely partially saturated with injected fluids.

中文翻译：

---

双差地震衰减层析成像方法及其在加利福尼亚间歇泉地热田中的应用

总结衰减结构的知识对于理解地下材料特性很重要。我们开发了一种双差地震衰减 (DDQ) 断层扫描方法，用于 3-D 衰减结构的高分辨率成像。我们的方法包括两个主要元素，事件对差分 ${t^*}$ ($d{t^*}$) 数据的反演和使用 $d{t^*}$ 数据的 3-D 衰减断层扫描。我们开发了一种新的光谱比方法，该方法联合反演来自在一组公共台站观察到的成对事件的光谱比数据，以确定 $d{t^*}$ 数据。光谱比方法消除了仪器和现场响应项，与使用单个光谱的传统方法的绝对 ${t^*}$ 相比，产生更准确的 $d{t^*}$ 数据。综合测试表明，使用我们的谱比方法对 $d{t^*}$ 数据的反演对源模型的选择和中等程度的噪声具有鲁棒性。我们修改了现有的速度断层扫描代码，以便它可以为 3-D 衰减结构反转 $d{t^*}$ 数据。我们将新方法应用于加利福尼亚州的间歇泉地热田，该地热田拥有以蒸汽为主的储层和悠久的注水历史。间歇泉的新 Qp 模型是使用 2011 年地震的 P 波数据确定的，使用我们更新的地震位置和 Vp 模型。通过利用更准确的$d{t^*}$数据和消除震源区以外公共路径上的模型不确定性，DDQ层析成像方法实现了更高的分辨率，特别是在震源区，与使用 ${t^*}$ 数据的标准断层扫描方法相比。这已通过真实和合成数据测试得到验证。我们的 Qp 和 Vp 模型显示了常温储层的一致变化，这可以通过压裂、渗透率和流体饱和度和/或蒸汽压力的变化来解释。与非常活跃的地震活动相关的显着的低 Qp 和 Vp 带在 2 公里以下深度的高温储层内成像。这个异常区域可能部分被注入的流体饱和。与非常活跃的地震活动相关的显着的低 Qp 和 Vp 带在 2 公里以下深度的高温储层内成像。这个异常区域可能部分被注入的流体饱和。与非常活跃的地震活动相关的显着的低 Qp 和 Vp 带在 2 公里以下深度的高温储层内成像。这个异常区域可能部分被注入的流体饱和。