Seismic Attenuation and Anisotropy in the Carpathians and Adjacent Basins: Upper Mantle Role in the Last Stages of Tethyan Closure

Raymond M.俄罗斯喀尔巴阡山弧标志着特提斯一个现已关闭的主要海湾的缝合线，特提斯是一个广阔的海洋盆地，曾经沿着欧亚大陆的南缘从地中海西部延伸到印度支那。 弧是独特的在几个方面：封闭的残余特提斯在这里需要一定程度的最近（中新世现在）大陆-大陆碰撞和消失，最有可能的是，一部分特提斯海洋岩石圈进入上地幔。 然而，喀尔巴阡构造的研究可能有广泛的应用，因为现在可见的过程一定发生在过去沿着历时闭合的特提斯边缘的其他地方。喀尔巴阡弧的Vranceabend带（北纬45.5度，25.5 E long.）关于它们的成因产生了争论：一个可行的构造情景是特提斯洋岩石圈的俯冲，其残余物被认为是刚刚从东欧和摩西地台的大陆岩石圈中分离出来。 第二种模型认为，海洋岩石圈俯冲在中新世晚期的某个时候结束，此后东欧或莫西地台大陆岩石圈的一部分一直沿着水平的岩石圈中部界面分层，并滴入上地幔。 Vrancea带下上地幔中高速“板”和低速软流层的预测分布在这些模型之间是不同的，可以通过层析成像（正在罗马尼亚进行，独立于本项目）和地震衰减和剪切波分裂的测量相结合来确定，这些测量描绘了冷岩石圈和暖软流层的分布，以及任何上地幔软流层的流动方向。 Vrancea的活动性可以通过测量地震衰减和剪切波分裂来确定板片分布和上地幔流动方向。 有针对性的测试地幔对特提斯闭合的反应将包括确定研究区域下地幔软流圈的存在和厚度，观测地幔流动方向，估计地震衰减和有关地幔温度场的相关推断，并最终对解释喀尔巴阡弧异常地震活动和火山活动的竞争性假设进行强有力的测试。 最后，对研究区域地震波传播和衰减的进一步了解将直接提高我们对这个人口稠密地区地震危险性的认识。

EAR-0230336Raymond M. RussoThe Carpathian arc marks the suture of a now-closed major embayment ofTethys, the expansive ocean basin that once stretched along the southernmargin of Eurasia from the western Mediterranean to Indochina. The arcis unique in several respects: Closure of the remnant Tethys here entailssome degree of very recent (Miocene-present) continent-continent collisionand disappearance of, most likely, a part of the Tethyan oceanic lithosphereinto the upper mantle. However, study of Carpathian tectonics may have wideapplication, since the processes now visible there must have taken placeelsewhere in the past along the diachronously closing Tethys margin.The unusual seismicity, volcanism, and surface deformation at the Vranceabend zone of the Carpathian arc (45.5 N lat., 25.5 E long.) has yieldeda debate about their cause(s): one viable tectonic scenario invokessubduction of a piece of Tethyan oceanic lithosphere, a remnant of whichis presumed to be just detaching from continental lithosphere of theEast European and Moesian platforms. A second model holds that oceaniclithosphere subduction ended some time in the late Miocene, and that sincethen a portion of East European or Moesian platform continental lithospherehas been delaminating along a horizontal mid-lithospheric interface anddripping down into the upper mantle. The predicted distribution of highvelocity `slab' and low velocity asthenosphere in the upper mantle beneathVrancea zone differs between these models and can be determined seismicallyby a combination of tomography (ongoing in Romania and independent of thisproject) and measurements of seismic attenuation and shear wave splitting,which delineate the distribution of cold lithosphere and warm asthenosphere,and the flow directions of any upper mantle asthenosphere. The activeseismicity at Vrancea can be exploited to delimit both slab distributionand upper mantle flow directions via measurements of seismic attenuationand shear wave splitting. Targeted tests of mantle responses to Tethysclosure will include establishment of the presence and thickness ofmantle asthenosphere beneath the study region, observations of mantleflow directions, estimation of seismic attenuation and associatedinferences concerning mantle temperature fields, and, ultimately, astrong test of competing hypotheses put forth to explain the unusualseismicity and volcanism of the Carpathian arc. Finally, improvedunderstanding of seismic wave propagation and attenuation in the studyregion will directly enhance our understanding of seismic hazard inthis populous area.--