The southeastern margin of the Tibetan Plateau is a crucial region to understand the mechanisms of plateau uplift and deformation.This region is seismically active and has experienced multiple large earthquakes,result...The southeastern margin of the Tibetan Plateau is a crucial region to understand the mechanisms of plateau uplift and deformation.This region is seismically active and has experienced multiple large earthquakes,resulting in significant human and economic losses.Constructing velocity and anisotropic tomography models is crucial for understanding the seismogenic mechanism and deep structural deformation in this area.In this study,we extract high-quality P-wave first-arrival data from the earthquake catalog of the China Earthquake Administration and use them to construct both common-receiver and commonsource differential traveltime datasets.We then apply a novel adjoint-state traveltime tomography approach to obtain new Pwave velocity and azimuthal anisotropy models for the region.This method eliminates the need for ray tracing,thereby reducing the potential bias from the ray theory and ray tracing.A comparison between our results and previous imaging models and shearwave splitting measurements reveals several new details.The results indicate weak anisotropy in the shallow depth of the central Chuandian block.Two low-velocity anomalies are identified beneath the Songpan-Ganzi and Lijiang-Xiaojinhe fault zones,as well as beneath the Xiaojiang Fault.The distinct anisotropic characteristics of these two low-velocity anomalies suggest different tectonic contexts:Beneath the Songpan-Ganzi and Lijiang-Xiaojinhe fault zones,the azimuthal anisotropy aligns north-south and northeast-southwest,while beneath the Xiaojiang Fault,it aligns northwest-southeast.In addition,the anisotropy of the upper mantle in the southern part of the study area has a significant east-west feature.The earthquake relocation results reveal intensified seismic activity in regions with significant velocity contrasts and near fault zones.Segmental seismic activity is observed along some major fault zones,and seismicity is also more pronounced in fault intersection areas.The new imaging results provide new perspectives and insights for understanding the seismogenic mechanisms and regional tectonic deformation in the region.展开更多
最小二乘逆时偏移(Least-Square Reverse Time Migration,LSRTM)相比于常规偏移具有更高的成像分辨率、振幅保幅性及均衡性等优势,是当前研究的热点之一.然而,目前LSRTM算法大多是基于二阶常密度标量声波方程建立的,忽略了密度变化对振...最小二乘逆时偏移(Least-Square Reverse Time Migration,LSRTM)相比于常规偏移具有更高的成像分辨率、振幅保幅性及均衡性等优势,是当前研究的热点之一.然而,目前LSRTM算法大多是基于二阶常密度标量声波方程建立的,忽略了密度变化对振幅的影响,因而基于振幅匹配策略的常规LSRTM很难在变密度介质下取得保真的成像结果.一阶速度-应力方程能够很好地处理变密度介质,但简单地将一阶速度-应力方程应用到LSRTM中缺乏理论基础.为此,本文从LSRTM的正问题入手,提出了基于交错网格的一阶速度-应力方程LSRTM理论方法.首先将一阶波动方程线性化,建立了一阶方程LSRTM的目标泛函,随后推导其伴随方程,并借助伴随状态法给出了迭代更新流程,最终建立了基于一阶速度-应力方程LSRTM的理论框架.进一步,通过在相位编码LSRTM中引入随机最优化思想,极大地减小了计算量、提高了计算效率.最后,通过模型试算验证了本算法的正确性和有效性.展开更多
基金supported by the National Key R&D Program of China(Grant No.2022YFF0800601)the China National Science and Technology Major Project(Grant 2024ZD1001101)。
文摘The southeastern margin of the Tibetan Plateau is a crucial region to understand the mechanisms of plateau uplift and deformation.This region is seismically active and has experienced multiple large earthquakes,resulting in significant human and economic losses.Constructing velocity and anisotropic tomography models is crucial for understanding the seismogenic mechanism and deep structural deformation in this area.In this study,we extract high-quality P-wave first-arrival data from the earthquake catalog of the China Earthquake Administration and use them to construct both common-receiver and commonsource differential traveltime datasets.We then apply a novel adjoint-state traveltime tomography approach to obtain new Pwave velocity and azimuthal anisotropy models for the region.This method eliminates the need for ray tracing,thereby reducing the potential bias from the ray theory and ray tracing.A comparison between our results and previous imaging models and shearwave splitting measurements reveals several new details.The results indicate weak anisotropy in the shallow depth of the central Chuandian block.Two low-velocity anomalies are identified beneath the Songpan-Ganzi and Lijiang-Xiaojinhe fault zones,as well as beneath the Xiaojiang Fault.The distinct anisotropic characteristics of these two low-velocity anomalies suggest different tectonic contexts:Beneath the Songpan-Ganzi and Lijiang-Xiaojinhe fault zones,the azimuthal anisotropy aligns north-south and northeast-southwest,while beneath the Xiaojiang Fault,it aligns northwest-southeast.In addition,the anisotropy of the upper mantle in the southern part of the study area has a significant east-west feature.The earthquake relocation results reveal intensified seismic activity in regions with significant velocity contrasts and near fault zones.Segmental seismic activity is observed along some major fault zones,and seismicity is also more pronounced in fault intersection areas.The new imaging results provide new perspectives and insights for understanding the seismogenic mechanisms and regional tectonic deformation in the region.
文摘最小二乘逆时偏移(Least-Square Reverse Time Migration,LSRTM)相比于常规偏移具有更高的成像分辨率、振幅保幅性及均衡性等优势,是当前研究的热点之一.然而,目前LSRTM算法大多是基于二阶常密度标量声波方程建立的,忽略了密度变化对振幅的影响,因而基于振幅匹配策略的常规LSRTM很难在变密度介质下取得保真的成像结果.一阶速度-应力方程能够很好地处理变密度介质,但简单地将一阶速度-应力方程应用到LSRTM中缺乏理论基础.为此,本文从LSRTM的正问题入手,提出了基于交错网格的一阶速度-应力方程LSRTM理论方法.首先将一阶波动方程线性化,建立了一阶方程LSRTM的目标泛函,随后推导其伴随方程,并借助伴随状态法给出了迭代更新流程,最终建立了基于一阶速度-应力方程LSRTM的理论框架.进一步,通过在相位编码LSRTM中引入随机最优化思想,极大地减小了计算量、提高了计算效率.最后,通过模型试算验证了本算法的正确性和有效性.
