摘要
从1996年丽江M_(S)7.0地震发生后至2023年8月,云南地区M≥6.7和M≥7.0地震出现了长达27.55 a的超长时间平静现象。本文从更大时空尺度上对该平静异常现象及其与青藏高原和川滇地块的强震活动之间的关系进行了分析和总结,并讨论了云南地区未来地震趋势。结果表明,1887年以来,云南地区5次M≥7.0地震平静期内其周边地震活动环境有很大差异性:第Ⅰ,第Ⅱ和第Ⅴ平静期出现在青藏高原M≥7.0地震活跃背景下(即云南地区平静,但青藏高原活跃),第Ⅲ和第Ⅳ平静期出现在青藏高原M≥7.0地震平静背景下(即云南地区平静,青藏高原也平静)。当前云南地区处于27.55 a超长时间平静期(即第Ⅴ平静期),其所处的周边地震活动环境与第Ⅰ和第Ⅱ平静期相似,据此推断,其后续地震趋势可能也与第Ⅰ和第Ⅱ活跃期相似,处于相对弱的活跃期。同时,未来较长时间青藏高原可能仍将处于M≥7.0地震活跃时段;2022年泸定M_(S)6.8地震后,川滇地块可能会进入M≥6.7地震活跃时段。
From the Lijiang M_(S)7.0 earthquake in 1996 to August 22,2023,a significant phenomenon of seismic quiescence has lasted for 27.55 years,which are the longest quiet period since 1900,both for M≥6.7 and M≥7.0 earthquakes in Yunnan Province.We further analyze and summarize the quiescence anomaly phenomenon of Yunnan’s strong earthquake and its relationship to the seismic status of the Qinghai-Xizang Plateau and Sichuan-Yunnan block on a larger spatio-temporal scale.Meanwhile,we discuss the future seismic trends in Yunnan region.Here are the conclusions.1)The energy released by all M≥5.0 earthquakes per year in Yunnan region is equival-ent to an M6.7 earthquake,which means an M6.7 represents the mean released energy per year,so we choose M6.7 as the lower limit of strong earthquake to study the seismicity in Yun-nan region.The retrospective analysis based on historical earthquakes indicates that the charac-teristics of active-quiet alternation in Yunnan region,Sichuan-Yunnan block,and Qinghai-Xizang Plateau,which are closely related to tectonic settings of M≥6.7 or M≥7.0 earth-quakes.Since 1887,there are four active-quiet alternative periods for M≥6.7 earthquakes in Yun-nan region,the active periods are 1913−1925,1936−1955,1970−1979,1988−1996 with the mean duration of(11.96±5.35)years,while the quiet periods are 1887−1913,1925−1936,1955−1970,1979−1988 with the mean duration(15.07±7.57)years.As for M≥7.0 earth-quakes,the active periods are 1913−1925,1941−1950,1970−1976,and 1988−1996 with the mean duration(8.40±2.12)years,while the quiet are 1887−1913,1925−1941,1950−1970,1976−1988 with the mean duration(18.58±5.87)years.The annual rate of occurrence is 0.42−0.83 times per year for M≥6.7 earthquakes and 0.27−0.63 times per year for the M≥7.0 earthquakes in Yunnan region.Since 1887,there have been two active-quiet alternative periods for M≥6.7 earthquakes in the Sichuan-Yunnan block,and the active periods are 1887−1925,1948−1996 with the mean duration(42.47±7.38)years,while the quiet periods are 1925−1948,1996−2022 with the mean duration(24.89±2.40)years.The annual rate of occurrence is 0.16−0.25 times per year for M≥6.7 earthquakes in Sichuan-Yunnan block.Since 1897,there have been three active-quiet alternative periods for M≥7.0 earthquakes in Qinghai-Xizang Plateau.The active periods are 1904−1956,1970−1976,and 1988 to now,while the quiet periods are 1897−1904,1956−1970,1976−1988 with the mean duration(10.88±3.26)years.The annual occurrence rate is 0.88−1.36 times per year for M≥7.0 earthquakes in Qinghai-Xizang Plateau.2)Since 1887,there have been significant differences in seismicity around Yunnan re-gion for its five quiet periods of M≥6.7 earthquakes.The quiescence periodsⅠ,Ⅱ,andⅤappeared under the background of the seismic activity of M≥7.0 earthquakes in Qinghai-Xizang Plateau,namely,seismic quiescence appeared in Yunnan region while activity in Qinghai-Xizang Plateau.However the quiescence periodsⅢandⅣappeared under the back-ground of the quiescence of M≥7 earthquakes in Qinghai-Xizang Plateau,namely both quies-cence in Yunnan region and Qinghai-Xizang Plateau.Currently,the periodⅤhas lasted for 27.55 years in Yunnan region,and the surrounding seismic activity is similar to that in the quiet periodsⅠandⅡ.Therefore we deduce the following seismic trend may be in relatively weak active periods,similar to the periodsⅠandⅡ.3)The comparison of seismicity between the Big Triangle area and Qinghai-Xizang Plat-eau shows that the active period(1904−1956)of M≥7.0 earthquakes in Qinghai-Xizang Plat-eau corresponds to the active period(1879−1957)of M≥8.0 earthquakes in Big Triangle area;from 1956 to 1988 there were two quiet periods in Qinghai-Xizang Plateau which correspond to the quiet period(1954−2001)in Big Triangle area,seismicity of M≥7.0 earthquakes in Qinghai-Xizang Plateau has been in an active period since 1988 while the seismicity of M≥8.0 earthquakes in Big Triangle area has come into a new active period since 2001.These seem to indicate that the active periods are consistent,as well as the quiet periods of M≥7.0 earth-quakes in Qinghai-Xizang Plateau and M≥8.0 earthquakes in the Big Triangle area.The ana-logy of the current and the period(1840−1957)of M≥8.0 earthquakes in the Big Triangle area suggests that the current active period of M≥7.0 earthquakes and M≥8.0 earthquakes in the Big Triangle area of East Asian continent will last for decades in the future.4)On September 5,2022,an M_(S)6.8 earthquake occurred in Luding,Sichuan Province.The earthquake was located on the Moxi fault,the southeast section of the Xianshuihe fault zone.The quiet period of M≥6.7 earthquakes that lasted for 26.59 years in the Sichuan-Yunnan block since 1996 has been terminated by the Luding M_(S)6.8 earthquake.The following seismicity may be a new active period of M≥6.7 earthquakes in the Sichuan-Yunnan block that analogizes the seismicity of quiet and active periods around 1948.5)Since 1997,all earthquakes with M≥7.0 in Qinghai-Xizang Plateau have concen-trated in the Bayan Har block except for several occurred in the Himalayan belt and Myanmar arc region.The retrospective analysis based on historical earthquakes indicates that the main region of seismic activity is alternative in the Sichuan-Yunnan block and Bayan Har block:Seismic activity appeared in the Bayan Har block while quiescence in the Sichuan-Yunnan block,by contrast,seismic activity appeared in the Sichuan-Yunnan block while less activity in Bayan Har block.Based on the inference,seismicity will be active in the Sichuan-Yunnan block and weak in the Bayan Har block after the Luding M_(S)6.8 earthquake in 2022.
作者
苏有锦
孙楠
赵小艳
贺素歌
张潜
Su Youjin;Sun Nan;Zhao Xiaoyan;He Suge;Zhang Qian(Yunnan Earthquake Agency,Kunming 650224,China)
出处
《地震学报》
CSCD
北大核心
2024年第2期242-256,共15页
Acta Seismologica Sinica
基金
国家重点研发计划(2021YFC3000705-08)
地震预测开放基金(XH23075D)
震情跟踪项目(2023010128)共同资助.
关键词
云南地区
强震平静
青藏高原
川滇地块
强震活动状态
Yunnan region
strong earthquake quiescence
Qinghai-Xizang Plateau
Sichuan-Yunnan block
active state of strong earthquakes
