Crustal Structure Beneath the Wabash Valley Seismic Zone From the Joint Inversion of Receiver Functions and Surface‐Wave Dispersion: Implications for Continental Rifts and Intraplate Seismicity
Crustal Structure Beneath the Wabash Valley Seismic Zone From the Joint Inversion of Receiver Functions and Surface‐Wave Dispersion: Implications for Continental Rifts and Intraplate Seismicity
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DOI：
10.1029/2018jb016989
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发表时间：
2019-07
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通讯作者：
Asiye Aziz Zanjani;Lupei Zhu;R. Herrmann;Yuchen Liu;Zhiyuan Gu;J. Conder
中科院分区：
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作者：
Asiye Aziz Zanjani;Lupei Zhu;R. Herrmann;Yuchen Liu;Zhiyuan Gu;J. Conder
北美中大陆几个板内地震带的地震活动被认为与现代应力场对前寒武纪大陆裂谷古断裂的重新激活有关。瓦巴什山谷地震带(WVSZ)下是否存在这样的裂谷系统尚不清楚。在这里，我们使用密集的线性地震台阵获得了横跨WVSZ的300公里长的剖面上的地壳结构图像。我们首先计算了台站的远震接收函数，并应用公共转换点叠加方法对地壳界面和莫霍面进行了成像。然后利用环境噪声互相关得到瑞利波和乐夫波的相速度和群速度。最后，我们联合接收函数和面波频散数据，确定了沿剖面的横波速度结构。结果表明，该区地壳厚度为50~60公里，具有典型的元古界地壳分层特征：显生界沉积层厚1~2公里，上地壳∼厚15公里，下地壳厚30~40公里。这张史无前例的高分辨率图像还显示了一个50公里宽的高速天体，位于隆起的莫霍面上方，以及拉萨尔变形带下方的上、中地壳的几个速度异常。我们将它们解释为前寒武纪末期失败的、未成熟的大陆裂谷中岩浆侵入产生的特征。WVSZ目前的地震活动可能是由于远场板块运动的应力场和该地区显著的地壳和上地幔不均质性的共同作用，使裂谷系统的古老断层重新激活。
Seismicity of several intraplate seismic zones in the North American midcontinent is believed to be related to reactivation of ancient faults in Precambrian continental rifts by the contemporary stress field. Existence of such a rift system beneath the Wabash Valley Seismic Zone (WVSZ) is not clear. Here we obtained a crustal structural image along a 300‐km‐long profile across WVSZ using a dense linear seismic array. We first calculated teleseismic receiver functions of stations and applied the Common‐Conversion‐Point stacking method to image crustal interfaces and the Moho. We then used ambient noise cross correlation to obtain phase and group velocities of Rayleigh and Love waves. Finally, we jointly inverted the receiver function and surface wave dispersion data to determine shear wave velocity structure along the profile. The results show a thick (50‐ to 60‐km) crust with a typical Proterozoic crustal layering: a 1‐ to 2‐km thick Phanerozoic sedimentary layer, an upper crust ∼15 km thick, and a 30‐ to 40‐km‐thick lower crust. The unprecedented high‐resolution image also reveals a 50‐km‐wide high‐velocity body above an uplifted Moho and several velocity anomalies in the upper and middle crust beneath the La Salle Deformation Belt. We interpreted them as features produced by magmatic intrusions in a failed, immature continental rift during the end of Precambrian. Current seismicity in WVSZ is likely due to reactivation of ancient faults of the rift system by a combination of stress fields from the far‐field plate motion and prominent crustal and upper mantle heterogeneities in the region.