川滇地块的震源力学机制、运动速率和活动方式
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摘要
用 4 4 2次中强地震的震源机制解分析了川滇次级地块应力场的优势方向。使用 771次 3级左右地震的滑动角λ参数统计确定震源断层的错动方式 ,并用中强地震P波初动解的N轴仰角的统计分布结果得到的震源断层错动或滑动型式去佐证。拟合中强地震的矩张量速率式 ,计算了川滇次级地块各地震构造区的年均滑动速率 ,并进行比较。根据 1980— 2 0 0 1年川青地块、雅江地块和滇中地块边界断裂带跨断层短水准、短基线定期复测结果 ,分析了水平和垂向年均形变速率。川滇地块间的运动是不均匀的。川青地块的运动方向为SEE。雅江地块压应力场优势方向为SSE ,相对川青地块的运动速率更大。滇中地块承袭雅江地块的运动方向 ,略偏东。密支那滇西地块压应力场有 2组优势方向 ,存在向NE方向的推挤和SSE方向的逃逸 ,活动速率大。
In this paper, Sichuan-Yunnan and its adjacent areas are divided into Yajiang, Central Yunnan, Sichuan-Qinghai, Central Sichuan, and Myitkyina-West Yunnan blocks. The mode and rates of motion of these blocks and their boundaries are studied separately. The predominant direction of the principal compressive stress axes within the blocks is analyzed in term of focal mechanism solutions of 442 moderate strong earthquakes. The models of focal faulting are determined through the rake angles λ obtained from source parameters of 771 events with magnitudes about 3 or more, and they are evidenced by focal faulting or slip modes derived from the distributions of N axis plunges of P-wave first motion solutions for moderate-strong earthquakes. A comparison is made between the moment tensor rates for moderate-strong earthquake and the calculated annual average slip rates of each seismotectonic zones within the blocks. Based on regular resurveying of across fault short level lines and baselines during the period of 1980-2001 along the border of the Sichuan-Qinghai, Yajiang and Central Yunnan blocks, the annual average rates of horizontal and vertical deformation for each site are analyzed. The motion rates of the Sichuan-Yunnan Block are inhomogeneous. The Sichuan-Qinghai Block moves toward SEE direction, and the predominant direction of the principal compressive stress axis falls in the range of N100°～130°E. The motion rate of this block is smaller than that of the Yajiang block, implying a delayed motion relative to that of the later. As a result, the Xianshuihe Fault between these two blocks displays a strong left lateral displacement. In addition to earthquakes of strike-slip type, the earthquakes of reverse dip-slip type are also predominant in the Sichuan-Qinghai Block. The predominant direction of the principal compressive stress axes in the Yajiang Block is within the range of N160°～170°E, i.e. SSE. The motion rate of this block is larger than that of the Sichuan-Qinghai Block, and the percentage of strike-slip type earthquakes in this block is larger then that in the other blocks. The motion direction of the Central Yunnan Block is nearly the same as that of the Yajiang Block, leaning slightly to the east. The predominant direction of the principal compressive stress axes in this block is in the range of N150°～160°E, and there are various types of earthquake failure including strike-slip, normal dip-slip, and reverse dip-slip. The direction of the principal compressive stress axes in the Central Sichuan Block falls in the range of N110°～140°E, approximately the same as the motion direction of the South China Block. The percentage of strike-slip type events in this block is relatively low, and there is a portion of events belonging to normal dip-slip or oblique dip-slip types. The motion rates at the northeast boundary between the Yajiang and Central Yunnan Blocks are greater than those at the west and south boundaries. The SSE-directed motion of the blocks is associated with right lateral component. Similarly, as the motion rates of the eastern boundary of the Sichuan-Qinghai Block is greater than that of the Longmenshan belt to the southeast of the block, the SSE-directed motion of the Sichuan-Qinghai Block is also associated with right lateral component. Two predominant directions of the principal compressive stress axes in the Myitkyina-West Yunnan Block indicate the NE-directed squeezing and the SE-directed escaping of the block, while the motion rate of the block is larger than that of the Yajiang and Central Yunnan Blocks. This might be attributed to the dynamic mechanism of the formation of collision and squeezing belts due to the direct action of the Asam Wedge while Indian Plate moving northward.
In this paper, Sichuan-Yunnan and its adjacent areas are divided into Yajiang, Central Yunnan, Sichuan-Qinghai, Central Sichuan, and Myitkyina-West Yunnan blocks. The mode and rates of motion of these blocks and their boundaries are studied separately. The predominant direction of the principal compressive stress axes within the blocks is analyzed in term of focal mechanism solutions of 442 moderate strong earthquakes. The models of focal faulting are determined through the rake angles λ obtained from source parameters of 771 events with magnitudes about 3 or more, and they are evidenced by focal faulting or slip modes derived from the distributions of N axis plunges of P-wave first motion solutions for moderate-strong earthquakes. A comparison is made between the moment tensor rates for moderate-strong earthquake and the calculated annual average slip rates of each seismotectonic zones within the blocks. Based on regular resurveying of across fault short level lines and baselines during the period of 1980-2001 along the border of the Sichuan-Qinghai, Yajiang and Central Yunnan blocks, the annual average rates of horizontal and vertical deformation for each site are analyzed. The motion rates of the Sichuan-Yunnan Block are inhomogeneous. The Sichuan-Qinghai Block moves toward SEE direction, and the predominant direction of the principal compressive stress axis falls in the range of N100°～130°E. The motion rate of this block is smaller than that of the Yajiang block, implying a delayed motion relative to that of the later. As a result, the Xianshuihe Fault between these two blocks displays a strong left lateral displacement. In addition to earthquakes of strike-slip type, the earthquakes of reverse dip-slip type are also predominant in the Sichuan-Qinghai Block. The predominant direction of the principal compressive stress axes in the Yajiang Block is within the range of N160°～170°E, i.e. SSE. The motion rate of this block is larger than that of the Sichuan-Qinghai Block, and the percentage of strike-slip type earthquakes in this block is larger then that in the other blocks. The motion direction of the Central Yunnan Block is nearly the same as that of the Yajiang Block, leaning slightly to the east. The predominant direction of the principal compressive stress axes in this block is in the range of N150°～160°E, and there are various types of earthquake failure including strike-slip, normal dip-slip, and reverse dip-slip. The direction of the principal compressive stress axes in the Central Sichuan Block falls in the range of N110°～140°E, approximately the same as the motion direction of the South China Block. The percentage of strike-slip type events in this block is relatively low, and there is a portion of events belonging to normal dip-slip or oblique dip-slip types. The motion rates at the northeast boundary between the Yajiang and Central Yunnan Blocks are greater than those at the west and south boundaries. The SSE-directed motion of the blocks is associated with right lateral component. Similarly, as the motion rates of the eastern boundary of the Sichuan-Qinghai Block is greater than that of the Longmenshan belt to the southeast of the block, the SSE-directed motion of the Sichuan-Qinghai Block is also associated with right lateral component. Two predominant directions of the principal compressive stress axes in the Myitkyina-West Yunnan Block indicate the NE-directed squeezing and the SE-directed escaping of the block, while the motion rate of the block is larger than that of the Yajiang and Central Yunnan Blocks. This might be attributed to the dynamic mechanism of the formation of collision and squeezing belts due to the direct action of the Asam Wedge while Indian Plate moving northward.
引文
车兆宏,张艳梅.2001.南北地震带中南段断层现今活动〔J〕.地震,21(3):31—37.
CHEZhao hong,ZHANGYan mei.2001.Currentfaultingactivityonthemiddle southsegmentoftheNorth southSeismicBelt〔J〕.Earthquake,21(3):31—37(inChinese).
陈健,陶本藻.1980.大地形变测量学(下册)〔M〕.北京:地震出版社.
CHENJian,TAOBen zao.1980.GeodeticSurvey(Volume2)〔M〕.SeismologicalPress,Beijing(inChinese).
陈天长,崛内茂木,郑斯华.2001.利用波初动和短周期振幅测定川滇地区地震震源机制解和应力场〔J〕.地震学报,23(4):436—440.
CHENTian chang,ShigekiHoriuchi,ZHENGSi hua.2001.EarthquakefocalmechanismsandstressfieldinSichuanYunnanareadeterminedusingPwavepolarityandshortperiodPandSwaveformdata〔J〕.ActaSeismologicaSinica,14(4):466—470.
成尔林.1981.四川及其邻区现代构造应力场和现代构造运动特征〔J〕.地震学报,3(3):231—241.
CHENGEr lin.1981.CurrenttectonicstressandtectonicmovementcharacteristicsofSichuananditsadjacentareas〔J〕.ActaSeismologicaSinica,3(3):231—241(inChinese).
程万正.1989.南北地震带的地震相关性与步进特征〔A〕.见:国家地震局科技监测司编.地震监测与预报方法清理成果汇编:测震学分册.北京:地震出版社.
CHENGWan zheng.1989.CorrelationandstepprogressivecharacteristicsofearthquakesontheNorth southSeismicBelt〔A〕.In:StateSeismologicalBureau(ed).VolumeofSeismometry.SeismologicalPress,Beijing(inChi nese).
程万正,陈天长.1994.1989年巴塘6.7级震群的复杂时空扩展和震源力学机制〔J〕.地震学报,16(2):153—159.
CHENGWan zheng,CHENTian chang.1994.Complextime spacespreadingandfocalmechanismofthe1989Batangearthquakeswarm(MS=6.7)〔J〕.ActaSeismologicaSinica,16(2):153—159(inChinese).
崔效锋,谢富仁.1999.利用震源机制解对中国西南及邻区进行应力分区的初步研究〔J〕.地震学报,21(5):513—522.
CHUIXiao feng,XIEFu ren.1999.ApreliminarystudyonstresszoningofsouthwestChinaandadjacentareasbyuseofearthquakemechanismsolutions〔J〕.ActaSeismologicaSinica,21(5):513—522(inChinese).
邓起东,张裕明,许桂林,等.1979.中国构造应力场特征及其与板块构造运动的关系〔J〕.地震地质,1(1):17—21.
DENGQi dong,ZHANGYu ming,XUGui lin,etal.1979.TectonicstressfieldcharacteristicsanditsrelationstoplatetectonicmotioninChina〔J〕.SeismologyandGeology,1(1):17—21(inChinese).
刁桂苓,于利明,宁杰远,等.1993.1989年大同震群的破裂特征〔J〕.地球物理学报,36(3):360—368.
DIAOGui ling,YULi ming,NINGJie yuan,etal.1993.Fracturecharacteristicsofthe1989Datongearthquakeswarm〔J〕.JournalofGeophysicalResearch,36(3):360—368(inChinese).
丁国瑜,卢演俦.1986.对我国现代板内运动状态的初步探讨〔J〕.科学通报,31(18):1412—1413.
DINGGuo yu,LUYan chou.1986.ApreliminaryresearchonthecurrentintraplatemotioninChina〔J〕.ChineseScienceBulletin,31(18):1412—1413(inChinese).
阚荣举.1977.我国西南地区现代构造应力场与现代构造活动特征的探讨〔J〕.地球物理学报,20(2):96—107.
GANRong ju.1977.StudyonthecurrenttectonicstressfieldandthecharacteristicsofcurrenttectonicactivityinsouthwestChina〔J〕.JournalofGeophysicalResearch,20(2):96—107(inChinese).
阚荣举.1980.西南地区现代构造应力场与板内强震活动〔J〕.地震研究,3(3):45—59.
GANRong ju.1980.CurrenttectonicstressfieldandstrongintraplateearthquakeactivityinsouthwestChina〔J〕.JournalofSeismologicalResearch,3(3):45—59(inChinese).
韩谓宾,夏大德.1980.松潘、平武地震与川青块体的运动〔J〕.地震科学研究,1(1):39—47.
HANWei bin,XIADa de.1980.SongpanPingwuearthquakeandthemotionofQinghaiSichuanblock〔J〕.Seis mologicalScientiaResearch,1(1):39—47(inChinese).
洪汉净,汪一鹏,沈军,等.2001.我国大陆地壳块体运动的平均图像及其动力学意义〔A〕.见:马宗晋,汪一鹏,张燕平主编.青藏高原岩石圈现今变动与动力学.北京:地震出版社.263—276.
HONGHan jing,WANGYi peng,SHENJun,etal.2001.Averagemotionpatternofblocksinthecontinentalcrustanditsdynamicmeaning〔A〕.In:MAZhong jin,WANGYi peng,ZHANGYan ping(Chiefed).Re centVariationandDynamicsoftheLithosphereundertheTibetanPlateau.SeismologicalPress,Beijing.263—276(inChinese).
李,汪良谋.1977.云南川西地区地震地质基本特征的探讨〔A〕.见:国家地震局西南烈度队编.西南地区地震地质及烈度区划探讨.北京:地震出版社.
LIPing,WANGLiang mou.1977.ResearchonbasicseismogeologicalcharacteristicsinYunnanandwestSichuanregion〔A〕.In:DiscussiononSeismogeologyandSeismicIntensityZoninginSouthwestChina(ed).Seismolog
CHEZhao hong,ZHANGYan mei.2001.Currentfaultingactivityonthemiddle southsegmentoftheNorth southSeismicBelt〔J〕.Earthquake,21(3):31—37(inChinese).
陈健,陶本藻.1980.大地形变测量学(下册)〔M〕.北京:地震出版社.
CHENJian,TAOBen zao.1980.GeodeticSurvey(Volume2)〔M〕.SeismologicalPress,Beijing(inChinese).
陈天长,崛内茂木,郑斯华.2001.利用波初动和短周期振幅测定川滇地区地震震源机制解和应力场〔J〕.地震学报,23(4):436—440.
CHENTian chang,ShigekiHoriuchi,ZHENGSi hua.2001.EarthquakefocalmechanismsandstressfieldinSichuanYunnanareadeterminedusingPwavepolarityandshortperiodPandSwaveformdata〔J〕.ActaSeismologicaSinica,14(4):466—470.
成尔林.1981.四川及其邻区现代构造应力场和现代构造运动特征〔J〕.地震学报,3(3):231—241.
CHENGEr lin.1981.CurrenttectonicstressandtectonicmovementcharacteristicsofSichuananditsadjacentareas〔J〕.ActaSeismologicaSinica,3(3):231—241(inChinese).
程万正.1989.南北地震带的地震相关性与步进特征〔A〕.见:国家地震局科技监测司编.地震监测与预报方法清理成果汇编:测震学分册.北京:地震出版社.
CHENGWan zheng.1989.CorrelationandstepprogressivecharacteristicsofearthquakesontheNorth southSeismicBelt〔A〕.In:StateSeismologicalBureau(ed).VolumeofSeismometry.SeismologicalPress,Beijing(inChi nese).
程万正,陈天长.1994.1989年巴塘6.7级震群的复杂时空扩展和震源力学机制〔J〕.地震学报,16(2):153—159.
CHENGWan zheng,CHENTian chang.1994.Complextime spacespreadingandfocalmechanismofthe1989Batangearthquakeswarm(MS=6.7)〔J〕.ActaSeismologicaSinica,16(2):153—159(inChinese).
崔效锋,谢富仁.1999.利用震源机制解对中国西南及邻区进行应力分区的初步研究〔J〕.地震学报,21(5):513—522.
CHUIXiao feng,XIEFu ren.1999.ApreliminarystudyonstresszoningofsouthwestChinaandadjacentareasbyuseofearthquakemechanismsolutions〔J〕.ActaSeismologicaSinica,21(5):513—522(inChinese).
邓起东,张裕明,许桂林,等.1979.中国构造应力场特征及其与板块构造运动的关系〔J〕.地震地质,1(1):17—21.
DENGQi dong,ZHANGYu ming,XUGui lin,etal.1979.TectonicstressfieldcharacteristicsanditsrelationstoplatetectonicmotioninChina〔J〕.SeismologyandGeology,1(1):17—21(inChinese).
刁桂苓,于利明,宁杰远,等.1993.1989年大同震群的破裂特征〔J〕.地球物理学报,36(3):360—368.
DIAOGui ling,YULi ming,NINGJie yuan,etal.1993.Fracturecharacteristicsofthe1989Datongearthquakeswarm〔J〕.JournalofGeophysicalResearch,36(3):360—368(inChinese).
丁国瑜,卢演俦.1986.对我国现代板内运动状态的初步探讨〔J〕.科学通报,31(18):1412—1413.
DINGGuo yu,LUYan chou.1986.ApreliminaryresearchonthecurrentintraplatemotioninChina〔J〕.ChineseScienceBulletin,31(18):1412—1413(inChinese).
阚荣举.1977.我国西南地区现代构造应力场与现代构造活动特征的探讨〔J〕.地球物理学报,20(2):96—107.
GANRong ju.1977.StudyonthecurrenttectonicstressfieldandthecharacteristicsofcurrenttectonicactivityinsouthwestChina〔J〕.JournalofGeophysicalResearch,20(2):96—107(inChinese).
阚荣举.1980.西南地区现代构造应力场与板内强震活动〔J〕.地震研究,3(3):45—59.
GANRong ju.1980.CurrenttectonicstressfieldandstrongintraplateearthquakeactivityinsouthwestChina〔J〕.JournalofSeismologicalResearch,3(3):45—59(inChinese).
韩谓宾,夏大德.1980.松潘、平武地震与川青块体的运动〔J〕.地震科学研究,1(1):39—47.
HANWei bin,XIADa de.1980.SongpanPingwuearthquakeandthemotionofQinghaiSichuanblock〔J〕.Seis mologicalScientiaResearch,1(1):39—47(inChinese).
洪汉净,汪一鹏,沈军,等.2001.我国大陆地壳块体运动的平均图像及其动力学意义〔A〕.见:马宗晋,汪一鹏,张燕平主编.青藏高原岩石圈现今变动与动力学.北京:地震出版社.263—276.
HONGHan jing,WANGYi peng,SHENJun,etal.2001.Averagemotionpatternofblocksinthecontinentalcrustanditsdynamicmeaning〔A〕.In:MAZhong jin,WANGYi peng,ZHANGYan ping(Chiefed).Re centVariationandDynamicsoftheLithosphereundertheTibetanPlateau.SeismologicalPress,Beijing.263—276(inChinese).
李,汪良谋.1977.云南川西地区地震地质基本特征的探讨〔A〕.见:国家地震局西南烈度队编.西南地区地震地质及烈度区划探讨.北京:地震出版社.
LIPing,WANGLiang mou.1977.ResearchonbasicseismogeologicalcharacteristicsinYunnanandwestSichuanregion〔A〕.In:DiscussiononSeismogeologyandSeismicIntensityZoninginSouthwestChina(ed).Seismolog
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