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

喀尔巴斯山弧线标志着特提斯湾一个现已关闭的主要海湾的缝合，特提斯湾是一个广阔的洋盆，曾经沿着欧亚大陆的南缘从地中海西部延伸到印度支那。Arcis在几个方面是独一无二的：这里残留的特提斯的闭合导致了某种程度的最近(中新世至今)的大陆-大陆碰撞，很可能是特提斯大洋岩石圈的一部分消失到上地幔。然而，对喀尔巴斯山构造的研究可能会有广泛的应用，因为现在可以看到的过程肯定发生在过去历时关闭的特提斯边缘的其他地方。喀尔巴斯山弧(北纬45.5度，东经25.5度)Vranceabend带的异常地震活动、火山活动和地表变形。引起了关于其原因的争论(S)：一种可行的构造情景是一块特提斯大洋岩石圈俯冲，据推测，这块岩石圈的残余物刚刚从东欧和莫斯地台的大陆岩石圈分离出来。第二种模式认为，海洋岩石圈俯冲作用在中新世晚期结束，此后部分东欧或莫斯地台大陆岩石圈沿水平的中-岩石圈界面剥离并向下滴入上地幔。Vrancea带上地幔中高速“板条”和低速软流圈的预测分布在不同的模型之间是不同的，可以通过地震层析成像(罗马尼亚正在进行的，与该项目无关)和地震衰减和横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。通过地震衰减和剪切波分裂的测量，可以利用Vrancea的活动性来圈定板块分布和上地幔流动方向。地幔对特提斯闭合响应的定向测试将包括确定研究区域下地幔软流层的存在和厚度，观测地幔流动方向，估计地震衰减和与地幔温度场有关的推断，并最终对提出的相互竞争的假设进行强有力的检验，以解释喀尔巴西安弧的异常地震和火山活动。最后，提高对研究区地震波传播和衰减的了解，将直接增强我们对这一人口稠密地区的地震危险性的了解。

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.--