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Shallow-depth acoustic reflection profiling survey has been conducted on the Tanlu fault zone in Laizhou Bay. It is found that the Tanlu fault zone is obviously active during the late Quaternary and it is still the dominating structure in this region. The Tanlu fault zone consists of two branches. The KL3 fault of the western branch is composed of several high angle normal faults which had been active during the period from the the latest Pleistocene to early Holocene, dissected by a series of northeast or approximate east-west trending fault which leaped sediment of the late Pleistocene. The Longkou fault of the eastern branch consists of two right-laterally stepped segments. Late Quaternary offsets and growth strata developed along the Tanlu fault zone verify that the fault zone retained active in the latest Pleistocene to the early Holocene. The Anqiu-Juxian fault that passes through the middle of Shandong and corresponds to the Longkou fault is composed of a series of right-laterally stepped segments. The active faults along the eastern branch of the Tanlu fault zone from the Laizhou bay to the north of Anqiu make up a dextral simple shear deformation zone which is characterized by right-lateral strike-slip movement with dip-slip component during the late Quaternary.

The Bohai Sea basin is located in the east to the Cenozoic rift basin of North China. It is a inner-land sea basin formed during Late Quaternary time. In this basin there are numerous active faults and many major earthquakes have occurred. Its major active tectonic zones are the northern section of the NE trending Yingkou-Weifang fault zone, Miaoxibei-Huanghekou-Linyi fault zone, and NW striking Beijing-Penglai fault zone, which intersect at the center of the Bohai Sea basin. These tectonic zones subdivide the sea area into four secondary neotectonic areas, which are subject to the recent tectonic stress field. Using the data of 38 focal plane solutions and 75 drill stress measurements, and the result of numerical modeling, we analyze the recent tectonic stress field of this region. Our result shows that this stress field is characterized by dominant horizontal or nearly horizontal stress. Its compressive stress is in the direction NE60°–90°, and the tensional stress is in NS-NW30°. There are some differences of principal stress between secondary tectonic areas. A remarkable feature of the Bohai Sea basin is a conjugate shear rupture zone, which develops in the crust and is the major seismogenic structure.

The September 17, 1303 Hongtong M=8 earthquake occurred in Linfen basin of Shanxi down-faulted basin zone. It is the first recorded M=8 earthquake since the Chinese historical seismic records had started and is a great earthquake occurring in the active intracontinental basin. We had held a Meeting of the 700th Anniversary of the 1303 Hongtong M=8 Earthquake in Shanxi and a Symposium on Intracontinental Basins and Strong Earthquakes in Taiyuan City of Shanxi Province on September 17–18, 2003. The articles presented on the symposium discussed the relationships between active intracontinental basins of different properties, developed in different regions, including tensional graben and semi-graben basins in tensile tectonic regions, compression-depression basins and foreland basins in compressive tectonic regions and pull-apart basins in strike-slip tectonic zones, and strong earthquakes in China. In this article we make a brief summary of some problems. The articles published in this special issue are a part of the articles presented on the symposium.