关键词: 重力基准, 陆态网络, 绝对重力测量, 重力变化速率

Abstract:

Based on the absolute gravity observation data of 10 gravity datum stations of the Crustal Movement Observation Network of China(CMONOC)in Yunnan and adjacent areas during 2010-2020, the gravity datum and its dynamic variation of each gravity datum station are obtained. The gravity variation trend of 9 stations at three different time scales and time periods shows that the gravity variation increased first and then decreased, and the turning point occurred around 2014, while Kunming Station is just the opposite. The Ludian M_S6.5, Yingjiang M_S6.1 and Jinggu M_S6.6 events occurred successively in 2014 when the gravity change increased to the turning point. Thereafter, the gravity change trend decreased until the occurrence of the Yangbi M_S6.4 earthquake in 2021. The results show that the variation of the gravity field in Yunnan and adjacent area is large and fast, and the transition period of increasing to decreasing is short and the variation trend is consistent. The gravity field change mechanism may be dominated by that the Qinghai-Tibetan plateau moves to the northeast caused by the push of Indian Plate, then is blocked by the Sichuan Basin, and the crustal material under the Qinghai-Tibetan plateau moves forward to Yunnan and its adjacent regions. The repeated observations of the absolute gravity survey network covering the whole country provide abundant and reliable data for obtaining the time-variable gravity field which is related to the crustal movement. Many scholars have done a lot of research on the results of the absolute gravity dynamic changes in the Chinese mainland, but the region is mainly focused on the Qinghai-Tibetan plateau, while the results of the absolute gravity dynamic change in other regions are still rarely revealed.

(1)The absolute gravity observation data of 10 gravity datum stations in Yunnan and Panzhihua from 2010 to 2020 show that except Kunming observation station, the gravity change trend increased first and then decreased, and the turning point occurred around 2014. Kunming station is the only station in the cave among the 10 observation stations, and its gravity change may be affected by the water content of the mountain. Five gravity observation campaigns at each observation station were carried out in different months of different years. Due to the lack of hydrological data at each observation station, the seasonal gravity change was not considered. Therefore, eliminating its influence is one of the important jobs in our future study.

(2)Earthquakes of M_S6.1, M_S6.5 and Ms6.6 occurred on May 31, August 3 and October 7, 2014 in Yingjiang, Ludian and Jinggu, Yunnan Province, respectively. The epicentral distances of all the gravity datum stations to the three events are more than 100km, so the coseismic gravity changes caused by events can be ignored.

(3)The Ludian M_S6.5, Yingjiang M_S6.1 and Jinggu M_S6.6 earthquakes occurred successively during the turning point period, and the gravity changes show a decreasing trend until the occurrence of the Yangbi M_S6.4 event in 2021. The mechanism of gravity field change of Yunnan and the adjacent areas may be as follows: The Qinghai-Tibetan plateau is pushed to the northeast by the Indian plate, then blocked by the Sichuan Basin, and the crustal material under the Qinghai-Tibetan plateau moves forward to Yunnan and its adjacent regions.

(4)Yunnan and the adjacent areas are characterized by complex tectonic environment and rapid seismic energy accumulation and release, which puts forward new demands for absolute gravity measurement mode, adding absolute gravity measurement stations and shortening observation period, so as to enhance the ability of more absolute gravity measurement to serve for monitoring the seismic activity and regional geological tectonic activity in Chinese mainland.

Key words: gravity datum, CMONOC, absolute gravity measurements, gravity change rate