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

喀尔巴阡山脉的弧线标志着特提斯（tethys）一个现已关闭的主要港湾的缝合线。特提斯是一个广阔的海洋盆地，曾经沿着欧亚大陆的南部边缘，从西地中海延伸到印度支那。这个弧在几个方面是独一无二的：残余特提斯的关闭在一定程度上导致了最近（中新世-现在）大陆与大陆的碰撞，最有可能的是，特提斯海洋岩石圈的一部分消失在上地幔中。然而，喀尔巴阡构造的研究可能有广泛的应用，因为现在在那里看到的过程一定发生在过去沿着历时性闭合的特提斯边缘的其他地方。喀尔巴阡弧（北纬45.5°）弗朗西隆起带异常的地震活动、火山活动和地表变形。（长25.5 E）引起了关于其成因的争论：一种可行的构造设想涉及到特提斯海洋岩石圈的一部分的俯冲，其残余物被认为刚刚从东欧和摩西地台的大陆岩石圈分离出来。第二种模式认为，海洋-岩石圈的俯冲作用在中新世晚期的某个时候结束了，从那时起，东欧或莫西亚台地大陆岩石圈的一部分沿着水平的岩石圈中部界面剥离，并向下滴入上地幔。这些模型对弗朗西亚带下上地幔高速“板块”和低速软流圈的预测分布有所不同，可以通过层析成像（罗马尼亚正在进行，独立于本项目）和地震衰减和横波分裂测量相结合的地震方法来确定，这些方法描绘了冷岩石圈和暖软流圈的分布，以及任何上地幔软流圈的流动方向。通过地震衰减和横波分裂测量，可以利用弗朗西亚的活动地震活动来划分板块分布和上地幔流动方向。对tethy闭合的地幔响应的目标测试将包括确定研究区域下地幔软流圈的存在和厚度，观察地幔流动方向，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不寻常的地震活动性和火山活动的竞争性假设进行强有力的测试。最后，提高对研究区域地震波传播和衰减的认识，将直接提高我们对这一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.--