Crustal structure using receiver function inthe east part of A’nyêmaqên suture belt
Abstract
Twenty broadband seismographs were deployed along Hongyuan, Sichuan to 英语论文范文Wuwei, Gansu. 81 teleseismic eventswere recorded in one year. We computed receiver functions from teleseismic waveform data and obtained S wavevelocity structure beneath each station along the profile by using receiver function inversion method. The resultsrevealed that the crustal structure is very complex and crustal average S wave velocity is to be on the low side.
Low velocity structure generally exists in the depth range of 10~40 km in the crust between Aba arc fault andnorthern edge fault of Qinling earth’s axis and it is a tectonic feature of complex geological process such as ancientA’nyêmaqên Tethys ocean from closing and side colliding to subducted plate exhumed or thrust rock slice lifted.
The Moho is about 50 km depth along the profile and is slightly deeper in the south than in the north.
Key words: A’nyêmaqên surture belt; receiver function; velocity structure
Introduction
Indian Plate and Eurasia Plate gathering action in Cenozoic Era formed Tibetan Plateau. Becauseof the gathering action continuously, Tibetan Plateau is still spreading outward and rising.
The NE Tibetan Plateau is a very important place where the colliding direction of the two plateschanged from the near S-N direction to the east and N-E direction and the eastward flowing materials
gathered, meanwhile the crust suffered from strong deformation. So it is very important tostudy the deep structure in NE Tibetan Plateau. Kunlun Mountain is divided into the western
Kunlun and the eastern Kunlun by Altyn tagh strike-slip fault, A’nyêmaqên suture belt belongs toeastern Kunlun, and it is one of important boundaries in the north Tibetan Plateau area.
Geophysical Exploration Center, China Earthquake Administration (GEC) carried out a near700 km long wide-angle reflection/refraction profile which passes through A’nyêmaqên suture belt.
The profile started from Barkam in Sichuan, ended at Gulan in Gansu, (ZHANG et al, 2007). Atthe same time, a broadband seismic linear array was deployed along this profile (Figure 1). In this
paper receiver functions were computed from the teleseismic P waveform data obtained from theseismic linear array and S velocity structure was determined by receiver function inversion.
∗ Received: 2007-04-09; accepted in revised form: 2007-07-24
Foundation item: National Natural Science Foundation of China (40334040 and 40474049).Contribution No. 200705, Geophysical Exploration Center, China Earthquake Administration.
Author for correspondence: [email protected]
5 14 ACTA SEISMOLOGICA SINICA Vol.20
Meanwhile we also discussed the crust and
uppermost mantle velocity structure and contact
relation between different geological tectonic
unit of A’nyêmaqên suture belt and its
two sides. The results will provide basic information
for establishing geodynamical model
of Tibetan Plateau rising mechanism.
The studied area covered two first-level
geological units (MA, 1989). About near the
post No. of 500 km, its northern part is
Sino-Korea paraplatform and the southern is
NE Tibetan Plateau. Still further, Sino-Korea
paraplatform can be divided into two secondary
tectonic units, Ordos block and Alxa
block. NE Tibetan Plateau in the studied area
also can be divided into three secondary geological
tectonic units, Qilianshan folding belt,
Qinling folding belt and Songpan-Garze orogenic
belt (Figure 1). A’nyêmaqên suture belt
is just located between Qinling fold belt and
Songpan-Garze orogen. From the south to the
north there are many faults passing through the
studied area, Aba arc fault, Hoh Sai Hu-Maqên
fault, Wudang-diebu fault, Zhouqu-liangdang
fault, northern edge fault of Qinling earth’s
axis and Riyueshan-Lajishan fault are large
scale faults among these faults. Songpan-Garze
orogenic belt is located between Aba arc fault
and Hoh Sai Hu-Maqên fault, A’nyemaqen
suture belt is located between Hoh Sai Hu-Maqên fa
