由富尔奈斯火山上的GEOSCOPE VBB台站得到的地倾斜信号

报道了距富尔奈斯火山顶8 km处的GEOSCOPE台网甚宽频带地震台观测到的甚长周期的瞬变过程。我们将地震台观测到的地面速度转换成地倾斜并通过与同一拱顶观测室内Blum型传统摆式倾斜仪记录的数据相比较检验了结果。通过比较表明,用水平地震仪测量周期小于25h的地倾斜是有效的。把这种方法用于1991年以来的几次火山喷发和岩浆侵入之前观测到的瞬变过程。由于GEOSCOPE台站到火山顶的距离适中,因而所得到的地傾斜观测值提供了有关火山喷发和岩浆侵入的信息,补充了火山顶部地倾斜观测网提供的有关岩浆源的形态和位置信息。     

Age of the Marwar Supergroup,NW India:A note on the U–Pb geochronology of Jodhpur Group felsic volcanics

The Marwar Supergroup(NW Peninsular India)is thought to be of Ediacaran-Cambrian age,based on previous paleontological and geochronological studies.However,direct constraints on the onset of sedimentation within the Marwar basin are still scarce.In this study,we report U–Pb zircon,LA-ICP-MS,and SIMS ages from the Chhoti Khatu felsic volcanic rocks,interlayered with the Jodhpur Group sandstones(Lower Marwar Supergroup).The cathodoluminescence images of the zircons indicate complex morphologies,and core-rim textures coupled with the wide range of ages indicate that they are likely inherited or in the case of thin poorly indurated ash-beds,detrital in origin.The age spectra of 68 zircon analyses from our sampling display a dominant 800–900 Ma age peak corresponding to the age of basement"Erinpura granite"rocks in the region.The youngest inherited zircon from a felsic ash layer yielded a U–Pb age of651 Ma±18 Ma that,together with previous studies and paleontological evidence,indicates a postCryogenian age for the initiation of Marwar sedimentation following a~125 Ma hiatus between the end of Malani magmatism and Marwar deposition.     

Anthropogenic Pressure on Structure and Composition of a Shola Forest in Kerala, India

Introduction Tropical region is endowed with a vast tract of diverse vegetation (Gentry 1992). Among different types of forests, the montane forests, due to their unique features including rich biodiversity andprominent ecological services, have always attracted biologists, bio-geographers, ecologists and forest managers (Doumenge et al. 1995). In India, montane forests covering 7.9 % of total forest area occur in the Himalayan, northeastern and southern parts of the country (Lal 1989). In s…     

模拟退火法反演远震P波波速慢度及方位数据求解长谷破火山口地壳速度结构

模拟退火法系一种非线性整体搜索算法,本文用以反演远震P波波速慢度和方位数据,求解地壳速度结构。综合试验表明,用模拟退火法能够以合理的精度确定P波低速带的空间位置,并能使近70％的目标速度扰动得以再现。实验表明,用少至两个台站的资料便可得到明显的结果。对长谷火山口的射线方向数据的反演发现,在8km深的再生穹丘构造以下存在一个不对称的低速带,相对背景波速有-25％的变动。这一低速带向东南延伸,深度至少达24km,其波速变动约为-10％。这些特征基本与远震走对的反演结果以及射线方向的正演模拟结果相一致,可能与长谷破火山口残余的岩浆房有关。