Recognition of Paleo-Tethys Suture Zone in eastern Myanmar

The site of final closure of Paleo-Tethys Ocean during the Triassic-Jurassic was marked by the colli-sional event between the Shan Massif and Indochina plate, in eastern Myanmar. Previous site of consumption of Paleo-Tethys is now occupied by a complex zone of suturing and deformation along Than Lwin River and in the east of it, formed by drastic tectonic evolution. It is geographically located approximately between longitudes 98E and 100E, and it extends northwards to Yunnan and southwards into West Thailand. The sigmoidal wrench struc-tures of suture zone is situated in the east of step-like structures of Shan Massif, and the western boundary of the suture zone must be immediately on the west side of Than Lwin River and the eastern boundary is near the east border of Myanmar. The area is largely covered by younger rocks of Paleozoic and Mesozoic age. The Upper Pa-leozoic units of Carboniferous to Permian comprise limestone and dolomite of the Plateau Limestone overlying unconformably the Lower Paleozoic rocks. Metasedimentary rocks of the Carboniferous and their metamorphic equivalents and the flysch-like Triassic-Jurassic units are found as folded and thrusted beds in the area. Large complex of granitic rocks of Late Triassic are also found. Metavolcanics, gabbro and a large number of chromite occur along with these units. A preliminary delineation of a suture zone as the site of closure of Paleo-Tethys Ocean in Myanmar territory is made for the first time and this zone is believed to be a tectonic linkage between Changning-Menglian belt of West China and Inthanon Zone of West Thailand.     

Historical tsunamis and storms recorded in a coastal lowland,Shizuoka Prefecture,along the Pacific Coast of Japan

Four sand units deposited by tsunamis and one sand unit deposited by storm surge(s) were identified in a muddy marsh succession in a narrow coastal lowland along the Pacific coast of central Japan. Tsunamis in ad 1498, 1605, 1707 and 1854 that were related to large subduction‐zone earthquakes along the Nankai Trough, and storm surges in 1680 and/or 1699 were responsible for the deposition of these sand units. These sand units are distinguished by lithofacies, sedimentary structures, grain‐size and mineral composition, and radiocarbon ages; their ages are supported by events in local historical records. The tsunami deposits in the study area are massive or parallel‐laminated sands, with associated intraclasts, gravels, draping mud layers and, rarely, a return‐flow subunit. The storm surge deposits are devoid of these characteristics, and are composed of groups of thin, current ripple‐laminated sand layers. The differences in sedimentary structures between the tsunami and storm surge deposits are attributed to the different characteristics of tsunami and storm waves.     

缅甸Tarlay 2011年地震与古特提斯缝合带的活动构造

An earthquake of 6.8 magnitude struck the eastern Shan State in Myanmar at 20:29:30 Myanmar Standard Time (01:55:12 PM UTC) on 24 March 2011. It is one of the earthquakes in plate-interior setting. Six after-shocks occurred the same year. The nucleation point of this earthquake was defined by an epicenter at 20 km west of Tarlay (20.705°N, 99.949°E) at a depth of 10 km and its magnitude was 6.8. The earthquake damage was disastrous. The geological disasters were linearly distributed along the surface rupture zone. The earthquake produced cracks, arch bend, erupting sand, gush water, etc. in many places. As a result of this strong earthquake, 224-305 houses were seriously damaged, 74 people were killed, 124 injured. The event was named after the nearest village Tarlay and the NE-or ENE-striking Nan Ma fault was responsible for it. A detailed morphotectonic study was carried out in the area using satellite image 1:24,000 scale aerial photographs and 1:63360 scale topographic maps, to correlate the seismicity with tectonics. It is found that there are two prominent lineaments striking in NE-or ENE- and N-S or NNE- SSW direction. The present-day deformation of the Than Lwin suture zone is consistent with roughly NW-SE extension and NE-SW striking compression, but with more conjugate strike-slip faulting and only minor normal faulting.