Information characteristics of ground fluid precursors of strong continental earthquakes

It has become seismologist's common view to attach importance to the study of the characteristics about the relationship among the space distribution of precursory anomalous stations, active structure, deep rock character, and different kinds of earthquakes. In this paper, the information characteristics of ground fluid precursors are analyzed with a few examples of earthquakes. The result shows that information characteristics of ground fluid precursors mainly demonstrate, temporally stage and acceleration pattern, specially, swarm and concurrence feature. It is a key scientific problem, we propose, to give deep study on the stage and concurrence pattern for realizing the seismogenic process as well as making relatively correct prediction to the potential earthquake focus and the occurrence time.

Continental dynamics and continental earthquakes

Two key research projects in geoscience field in China since the IUGG meeting in Birmingham in 1999, the project of East Asian Continental Geodynamics and the project of Mechanism and Prediction of Strong Continental Earthquakes are introduced in this paper. Some details of two projects, such as their sub-projects, some initial research results published are also given here. Because of the large magnitude of the November 14, 2001 Kunlun Mountain Pass MS=8.1 earthquake, in the third part of this paper, some initial research results are reviewed for the after-shock monitoring and the multi-discipline field survey, the impact and disaster of this earthquake on the construction site of Qinghai-Xizang (Tibet) railway and some other infrastructure.

Below-Moho Earthquakes of Tibet,Himalaya,the Indian Foreland,and Worldwide:How,Where and Why?

We seek to understand lithospheric rheology by mapping continental earthquake depths relative to Moho depth,across the entire India/Asia convergent orogen,and eventually worldwide.Such mapping has particular value in geothermometry,and potentially in identifying regions of delamination.How:We are extending our Sn/Lg method beyond amplitude ratios of regional seismic phases measured on arrays(array Sn/Lg method,Wang and Klemperer,2021)to include frequency proxies for earthquake depth relative to Moho(Wang&Klemperer,2024a,b;Harris et al.,2024).

The Active Yakutat （Kula？） Plate and Its Southcentral Alaska Megathrust and Intraplate Earthquakes

Alaska geology and plate tectonics have not been well understood due to an active Yakutat plate, believed to be part of the remains of an ancient Kula plate, not being acknowledged to exist in Alaska. It is positioned throughout most of southcentral Alaska beneath the North American plate and above the NNW subducting Pacific plate. The Kula？ plate and its eastern spreading ridge were partially ＂captured＂ by the North American plate in the Paleocene. Between 63 Ma and 32 Ma, large volumes of volcanics erupted from its subducted N-S striking spreading ridge through a slab window. The eruptions stopped at 32 Ma, likely due to the Pacific plate fiat-slab subducting from the south beneath this spreading ridge. At 28 Ma, magmatism started again to the east; indicating a major shift to the east of this ＂refusing to die＂ spreading ridge. The captured Yakutat plate has also been subducting since 63 Ma to the WSW. It started to change to WSW fiat-slab subduction at 32 Ma, which stopped all subduction magmatism in W and SW Alaska by 22 Ma. The Yakutat plate subduction has again increased with the impact/joining of the coastal Yakutat terrane from the ESE about 5 Ma, resulting in the Cook Inlet Quaternary volcanism of southcentral Alaska. During the 1964 Alaska earthquake, sudden movements along the southcentral Alaska thrust faults between the Yakutat plate and the Pacific plate occurred. Specifically, the movements consisted of the Pacific plate moving NNW under the buried Yakutat plate and of the coastal Yakutat terrane, which is considered part of the Yakutat plate, thrusting WSW onto the Pacific plate. These were the two main sources of energy release for the E part of this earthquake. Only limited movement between the Yakutat plate and the North American plate occurred during this 1964 earthquake event. Buried paleopeat age dates indicate the thrust boundary between the Yakutat plate and North American plate will move in about 230 years, resulting in a more ＂continental＂ type megathrust earthquake for southcentral Alaska. There are, therefore, at least two different types ofmegathrust earthquakes occurring in southcentral Alaska： the more oceanic 1964 type and the more continental type. In addition, large ＂active＂ WSW oriented strike-slip faults are recognized in the Yakutat plate, called slice faults, which represent another earthquake hazard for the region. These slice faults also indicate important oil/gas and mineral resource locations.

Review on study of seismotectonics in China

This paper reviews briefly the progresses made during the last four years (1999~2002) in study of seismotectonics in China, especially appraises the achievements in the fields of the crustal and upper mantles structure, the active faults and tectonic setting of large earthquakes, the crustal deformation, and the numerical simulation. Most earthquakes occurred in China belong to continental earthquakes. Therefore, Chinese seismologists pay more attention to the continental earthquakes. Based on improvements of the observation systems in China during the ninth Five-Year Plan, the studies on seismotectonics have achieved great progresses.

Gravity variation before the Akto Ms6.7 earthquake, Xinjiang

The relationship between gravity variation and the Akto Ms6.7 earthquake on November 11, 2016, was studied by use of mobile gravity observation data from the China continental structural environmental monitoring network. The result revealed that before the Akto earthquake, a high positive gravity variation was observed in the Pamir tectonic knots region （within a maximum magnitude of approximately ＋80 microgal）, which was consistent with the existing knowledge of gravity abnormality and the locations of strong earthquakes. In view of the recent strong seismic activities in the Pamir tectonic knots region, as well as the strong upward crust movement and compressive strain, it is believed that gravity change in the Pamir tectonic knots region reflects the recent strong seismic activities and crust movement.