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J. Phys. Earth, 34, Suppl., S111-S127, 1986 CRUSTAL DEFORMATION BEFORE STRONG EARTHQUAKES AND UTILITY OF EARTHQUAKE PREDICTION BY GEODETIC MEASUREMENTS: EXTENDED ABSTRACT Zusheng ZHANG,Shaofen YING, and Yongjian SHEN Geodetic Brigade, State Seismological Bureau, Tianjin, China (Received June 22, 1985) 1. Introduction The preseismic deformation data of 10 major earthquakes that occurred in mainland China are collected and analyzed in this paper. We hope to clarify the characteristics of crustal deformation in the preparatory process of strong earthquakes and to evaluate the monitoring and predicting of earthquakes by available geodetic means. Earthquake studies show that preparatory process and occurrence of a major shallow earthquake always seem to be accompanied by crustal surface deformation. The defor- mation data obtained in large areas by available geodetic means have now been widely used in research on crustal motion and earthquake prediction. Therefore, the characteristics of crustal deformation prior to a large earthquake and whether an earthquake can be correctly detected and predicted with geodetic data, have become a matter of great interest. In this paper, the data of crustal deformation preceding 10 major Chinese earthquakes (Table 1 and Fig. 1; MA et al., 1982) have been collected and checked or reprocessed. We hope to obtain some characteristics of crustal deformation before an earthquake by analyzing these data and making an appropriate evaluation of the role played by crustal deformation measurements in earthquake prediction. 2. Preseismic Deformation 2.1 The Dongchuan earthquakes of February 5 and 13, 1966 (MS=6.5, 6.2) The Dongchuan earthquakes occurred in the Xincun Quaternary graben. On the west margin of the basin, the Xiaojiang deep fault outcrops discontinuously. The Cenozoic tectonic movement is very intense here and the earthquakes occurred right near the intersection of a few faults (Fig. 2). There is only a little preseismic releveling data, but they show that the Xincun basin subsided by 25 mm between 1958 and 1963 as compared with the surrounding area. It seems to coincide with the remarkable subsidence of the basin during the earthquake and reflects an inheritance of earlier movement. The triangulation data show dilatation near the epicenter and compression far away from the epicenter before the event (Fig. 3). S111 S112 Z. ZHANG,S. YING, and Y. SHEN Table 1. Ten major earthquakes in China. Fig. 1. The map of distribution of the epicenters of 10 major Chinese earthquakes. Crustal Deformation before Strong Earthquakes S113 Fig. 2Fig. 3 Fig. 2. Simplified tectonic map of the Dongchuan region. Fig. 3. The distribution of strain before the earthquake. Fig. 4. Simplified tectonic map of the Xingtai region. The locations of bench marks numbered 449 and 454 (see Fig. 5) are shown. The Fuyang River shown by the thin line flows from south to northeast. 2.2 The Xingtai earthquakes of March 8 and 22, 1966 (MS=6.8, 7.2) The Xingtai earthquakes occurred in the Shulu graben (Fig. 4). The preseismic releveling data show obvious subsidence in the Shulu graben (Fig. 5), which is consistent S114 Z. ZHANG, S. YING, and Y. SHEN Fig. 5. Vertical deformation profile of the leveling line along the Fuyang River (GEODETICSURVEY BRIGADE FOR EARTHQUAKE RESEARCH, 1975 a). The right-hand- side of the figure shows the upriver side. Fig. 7. Vertical deformation profile of the leveling line from Gaoyi to Datianzhuang (see Fig. 4). Elevation changes relative to the results for the survey in 1965 are shown. Crustal Deformation before Strong Earthquakes S115 with the movements during and after the earthquakes. In Fig. 6, the change of bench mark No. 449 represents the subsidence of the graben, but bench mark No. 454 shows the relative uplift of the Xingjiawan region. During the 10 years before the earthquake, the average rate of relative movements decreased quite significantly. In addition, leveling data of 3 epochs observed in the direction perpendicular to the fault indicate that in the region outside the graben, no obvious crustal deformation was detected from 1958 to just a few days before the M=6.8 earthquake in 1966 (Fig. 7). It suggests that significant preseismic crustal deformation was localized within the Shulu graben which stretches for 70 to 100 km in the NNE direction, and its width is not more than 20 to 30 km in the NWW direction. 2.3 The Hejian earthquake of March 27, 1967 (MS=6.3) The Hejian earthquake took place in the NNE-trending Litan graben in the North China plain (Fig. 8). The profile of vertical deformation along the Fuyang River is plotted in Fig. 9 and shows the subsidence of the Litan graben. It is similar to that of the Xingtai earthquake (Fig. 5), but is not as typical as the latter, because this area is covered by thick Fig. 8. Simplified tectonic map of the Hejian region. The Fuyang River shown by the thin line flows from southwest to northeast. Fig. 9. Vertical deformation profile of the leveling line along the Fuyang River. The right-hand side shows the upriver side. S 116Z. ZHANG, S. YING, and Y. SHEN soil and the contamination due to ground water movement cannot be neglected. 2.4 The Yangjiang earthquake of July 26, 1969 (MS=6.4) The tectonic background of the Yangjiang earthquake is the uplift of the NNE- trending Mt. Longgao-Mt. Luoqing region. There is only one leveling line running through the neighbourhood of the epicenter. The profile of the leveling line shows that the area near the epicenter has uplifted significantly (Figs. 10 and 11). Fig. 10. Simplified tectonic map of the Yangjiang region. Fig. 11. Vertical deformation profile of th e leveling line. Crustal Deformation before Strong Earthquakes S117 Fig. 12. Simplifie d tectonic map of the Tonghai region. Fig. 13. Vertical deformation profile of the leveling line during 1958 to 1969 (from Daliyuan to Jianshui) (GEODETICSURVEY BRIGADE FOR EARTHQUAKE RESEARCH, 1975 b). 2.5 The Tonghai earthquake of January 5, 1970 (MS=7.7) The Tonghai earthquake occurred on the Qujiang fault in the southern part of the Diandong (east Yunnan) and Dianzhong (central Yunnan) fault blocks (Fig. 12). It is a tectonically complicated area where stress can be easily accumulated and released. S118 Z. ZHANG, S. YING, and Y. SHEN Fig. 14. Vertical deformation profile of the leveling line Kunming to Yongwu). during1955 to 1958 (from Fig. 15 Fig. 16 Fig.15. Simplified tectonic map of the Liaonan region. 16. Vertical deformation of the Liaonan regionFig. during 1958-1970. The numbers show uplift in milimeters (GEODETICSURVEY BRIGADE FOR EARTHQUAKE RESEARCH , 1977). There are two leveling lines running through the epicentral region. The preseismic vertical deformations revealed by both lines are shown in Figs. 13 and 14. They show that a subsidence zone might exist along the fault and it is this zone that sank rapidly during this event. 2.6 The Haicheng earthquake of February 4, 1975 (Ms=7.3) The Haicheng earthquake occurred at a place where the Liaodong rise platform (east of Liao River flowing from northeast to southwest down to Yingkou) and the Mesozoic- Cenozoic down-faulting region of lower Liao River intersect. There are two principal faults here, one is the NE-striking Haicheng-Jinzhou fault and another is the NW-trending Xiaogushan-Xiuyan buried fault. The two faults form a T-shape near Haicheng. The Crustal Deformation before Strong Earthquakes S119 Fig. 17. The anomalous precursors detected by short-line leveling at the Jinxian station (see Fig. 15 for its location) (GEODETICSURVEY BRIGADE FOR EARTHQUAKE RESEARCH,1977). The upward motion indicates relative uplift of the NWW end of the short leveling line, which is 560 m long. Fig. 18 Fig.Fig. 18.19. Simplified tectonic map of the Longling region. Elevation variation of the leveling line (Tengchong—Mangshi).Fig. 19. earthquake occurred right on the latter and 20 km away from the former. It might be the rupture of the locked section of the latter fault (Fig. 15). This earthquake is well known, because it was successfully predicted and the anomalous deformation provided one of the bases for the prediction. Prior to the earthquake, the lower Liao River plain (the northwestern part of Fig. 16) kept subsiding and the mountain region in the east Liaoning Province kept uplifting (GEODETICSURVEY BRIGADEFOR EARTHQUAKE RESEARCH, 1977). The maximum rate of vertical uplift was S120 Z. ZHANG, S. YING, and Y. SHEN 3 mm per year from 1937 to 1958 and 5 mm per year from 1958 to 1971. And the earthquake occurred where contours are bent convex northward (Fig. 16). It should be noted that from 1973 to 1975, before the earthquake, deformation near the epicentral region was not great, while at the Jinxian station (see Fig. 15), on the south end of the Haicheng-Jinzhou fault 200 km away from the epicenter, the anomalous precursors detected by short-line leveling had lasted for 17 months (Fig. 17). 2.7 The Longling earthquakes of May 29, 1976 (Ms=7.3, 7.4) The Longling earthquakes took place within a granite body surrounded by the faults of Nu River (striking NNW), Wanding (striking EW), and Longling-Ruili (striking NE) in Southwest Yunnan. It is a quasi-uniform massive rock body in which there are no large faults, but only some small NNW- and NEE-trending fracture zones (Fig. 18). The data of Tengchong-Mangshi leveling line running through the neighborhood of the epicenter show that there is a subsidence in the section crossing the Longling-Ruili fault (CHEN,1979). The maximum subsidence occurred within the Longling basin on the margin of the granite rock body, indicating movement of the granite body relative to the sur- rounding areas (Fig.

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