摘要
美国西北部的卡斯卡迪亚是典型的暖俯冲带,在其沿岸地区观测到大量非火山震颤,呈不均匀分布.非火山震颤的发生与俯冲带中流体引发的孔隙压力升高有关,然而,该地区流体分布和运移模式一直存在争议.在震颤区附近弧火山活动减弱,甚至缺失,其减弱的原因也不清楚.由于壳内熔体或流体会导致地震Pg波振幅的显著衰减,因此通过Pg波Q值成像能够提供对地壳流体分布的约束.本研究收集了卡斯卡迪亚俯冲带623个台站记录的地壳Pg波波形资料,构建了宽频带衰减模型,分辨率达到0.5°×0.5°.成像结果显示,在震颤密集区西侧存在两个强衰减异常区,可能指示地壳内流体富集.卡斯卡迪亚沿岸“强-弱-强”分段式衰减结构与震颤的分布高度吻合,与“低-高-低”的速度和电阻率观测保持一致,说明壳内流体赋存形态的横向不均匀性.具有较低的渗透率的Siletzia地体表现为弱衰减特征,可能阻碍了流体运移,导致震颤强度减弱和复发周期增大.浅部流体聚集可能导致进入深部地幔楔的流体较少,抑制了熔体的产生,因而在震颤区附近弧火山活动减少.
Cascadia in the northwestern United States is a typical warm subduction zone,where many nonvolcanic tremors are unevenly distributed along the coastal region.These tremors are associated with elevated pore pressure induced by fluids within the subduction system.However,the distribution and migration patterns of these fluids remain debated.Arc volcanism near tremor zones is often absent or diminished and poorly understood.Since melts and fluids significantly attenuate seismic Pg-wave amplitudes,Pg-wave Q tomography can constrain the crustal fluid distribution.In this study,we collected Pg waveforms recorded at 623 stations across the Cascadia subduction zone and constructed a broadband crustal attenuation model with a resolution of 0.5°×0.5°.The imaging result reveals two strong attenuation anomalies west of the dense tremor zones,indicating fluid accumulation in the crust.Along the Cascadia margin,a“strong-weak-strong”segmented attenuation pattern closely correlates with the tremor distribution.It aligns with previously identified“low-highlow”velocity and resistivity structures,suggesting significant lateral heterogeneity in crustal fluid content.The Siletzia terrane with low permeability exhibits weak attenuation,which may impede fluid migration and contribute to reduced tremor intensity and longer recurrence intervals.Shallow fluid accumulation may limit transport to the deeper mantle wedge,thereby suppressing melt generation and reducing arc volcanic activity near the tremor zones.
作者
杨庚
赵连锋
杨英杰
谢小碧
李若婕
姚振兴
YANG Geng;ZHAO LianFeng;YANG YingJie;XIE XiaoBi;LI RuoJie;YAO ZhenXing(Department of Earth and Space Sciences,Southern University of Science and Technology,Shenzhen Guangdong 518055,China;Key Laboratory of Planetary Science and Frontier Technology,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing100029,China;Colloge of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Heilongjiang Mohe Observatory of Geophysics,Institute of Geology and Geophysics,Chinese Academy of Sciences,Mohe Heilongjiang165300,China;Institute of Geophysics and Planetary Physics,University of California at Santa Cruz,CA 95064,USA)
出处
《地球物理学报》
2025年第10期3810-3822,共13页
Chinese Journal of Geophysics
基金
国家自然科学基金(42430306,42404067)
中国博士后科学基金(2024M751295)
国家资助博士后研究人员计划(GZC20240638)联合资助.
作者简介
第一作者:杨庚,男,1997年生,博士后,主要研究方向为地震学.E-mail:yangg@sustech.edu.cn;通讯作者:赵连锋,男,1972年生,研究员,主要研究方向为地震学.E-mail:zhaolf@mail.iggcas.ac.cn。
