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地震前长周期事件的研究——历史与现状 总被引：16，自引：1，他引：15
自20世纪60年代以来,已经积累了许多地震前长周期事件的观测资料。这些长周期事件可以被很多不同的观测系统记录到,如跨断层形变、超低频电磁异常、次声波异常、井下低频导波、井水水位等。理论上对地震前长周期事件已给出了许多论证,例如,震前的断层蠕动、静地震与慢地震、断层的断裂预扩展和地震成核等。解决震前长周期事件的地面可测性,对突破“震前平静”带来的短临预测的困惑会起到举足轻重的作用。目前的主要问题是缺乏网络化的系统观测和对物理机制的研究。 相似文献
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井水位长周期事件记录及其机理的讨论 总被引：13，自引：1，他引：12
选择了几口具有代表性的观测井, 并对这些井孔在强震前记录到长周期波现象的特征进行了分析。从理论上对地震前的长周期事件给出了较为合理的解释, 认为地震前一些敏感井水位长周期事件可能反映了断层蠕动、静地震与慢地震、断裂的预扩展和地震成核等。井— 含水层系统像一个长周期地震仪, 它为记录到有价值的前兆低频波提供了最佳的频率响应范围。 相似文献
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Aki (1969) first modeled coda waves of a local earthquake as a superposition of scattered surface waves. This paper attempts
to clarify the constituents of surface-wave coda at long periods at very long lapse times. For a large earthquake of magnitude
7 or larger, vertical component oscillation in periods from 90 to 180 s persists for more than 20 hours from the earthquake
origin time. Although the early portion of the coda envelope is successfully modeled by assuming incoherent scattered Rayleigh
waves by heterogeneities distributed all over the Earth, the later potion of the observed coda envelope (roughly later than
35,000 s) has systematically larger amplitude than theoretical prediction. To clarify the cause of this discrepancy, we studied
the constituents of vertical-component seismograms of three large earthquakes recorded by the F-net in Japan using the f-k power spectral analysis. We found that the direct and scattered fundamental-mode Rayleigh waves of velocity about 3.7 km/s
are dominant in the earlier part of each envelope. It justifies the use of a scattering model of the fundamental Rayleigh
waves for synthesizing the envelope. At lapse times later than 20,000 s–35,000 s, higher modes with phase velocities around
20 km/s become dominant. The transition time to the dominance of higher modes is found to become earlier for a deeper focus
earthquake. The small coda attenuation factor from (1.90±0.23) × 10−3 to (2.38±0.32) × 10−3 estimated from later coda envelopes recorded at IRIS stations distributed worldwide also agrees with the attenuation factor
of spheroidal modes according to PREM. We may interpret that higher mode waves are uniformly distributed at large lapse time
due to large velocity dispersion and/or scattering and they dominate over the fundamental mode waves because of smaller attenuation
in the lower mantle. The coda attenuation measurement proposed by Aki is found to be useful even for long periods and at very
large lapse times. 相似文献
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中强地震序列的主震发生后，短时间内受台站距震中较远、尾波干扰和波形重叠等因素的影响，往往会遗漏大量的地震，而地震目录的完整性会直接影响到震后趋势判定和余震序列特征分析的科学性和可靠性。本文利用基于GPU加速的模板匹配方法对2017年8月1～12日的连续波形进行扫描计算，检测九寨沟MS7.0地震前后遗漏的地震事件，选取台网目录中信噪比较高的1033个地震事件作为模板，在主震前7天至震后5天期间识别出4854个检测地震事件，为台网可定位目录的3.3倍，除去对台网单台地震事件的修正外，还检测到1797个遗漏地震事件，将完备震级从1.6级降低到1.4级。基于补充了遗漏地震的完整地震目录，对2017年8月8日九寨沟MS7.0地震序列活动特征进行分析。结果表明，前震序列在主震前短时间内出现了地震活动的密集增强，b值也显示为低值状态，可能是深部断层发生破裂之前的加速蠕动的结果。随着时间的推移，余震序列的完备震级逐渐下降并趋于稳定，b值存在缓慢升高的趋势，未来较长时期内余震序列仍将处于持续衰减的状态。 相似文献
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张北地震前小震活动和余震序列精确定位及主震破裂方向的讨论 总被引：3，自引：0，他引：3
1970年至1998年1月10日张北地震前,沿NWW向发生2级以上地震24次,其分布相对集中,呈条带状。对华北台网所记上述地震的到时数据全部重新查图核对,并补充了内蒙古台网5个台的数据以改善用于定位的台站分布,并采用主地震定位法重新定位,除一个地震外,其余地震更加集中,形成一小震条带。1998年2月中国地震局地球物理勘探中心在张北震区架设10台短周期数字化地震仪,记录了大量微震。作者采用P波和S波到时差重新进行了震源定位,得到184次微震的定位结果,连同1998年1～2月张北震区3级以上地震事件定位结果一起勾画出6．2级地震的震源破裂带。由张北地震震中向SEE向延伸存在由强震构成的张家口渤海地震带。根据精确定位结果,结合修订后主震的震源机制、宏观烈度分布和层析成像资料,讨论了张北地震和小尺度地震带(震源破裂带)、震前的中等尺度小震条带以及大尺度的张家口-渤海强震带的关系。 相似文献
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2022年1月8日青海省海北州门源县发生MS6.9地震,震中距离2016年1月21日门源MS6.4地震震中约33km,两次门源地震均发生在冷龙岭断裂附近,但在震源机制、主发震断层破裂过程及地震序列余震活动等方面显著不同。针对两次门源地震序列的比较分析,对研究冷龙岭断裂及其附近区域强震序列和余震衰减特征等具有重要研究意义。通过对比分析2022年门源MS6.9地震和2016年门源MS6.4地震余震的时空演化特征,发现二者在震源过程和断层破裂尺度上存在明显差异,前者发震断层破裂充分,震后能量释放充分,余震丰富且震级偏高;而后者发震断层未破裂至地表,余震震级水平偏低。综合分析两次门源地震序列表现出来的差异性,认为其可能与地震发震断层的破裂过程密切相关,且同时受到区域构造环境的影响。 相似文献
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1997年9月三水地震震相特征与发震构造 总被引：2，自引：0，他引：2
１９９７年９月广东省三水市发生的ＭＬ３．７、４．４级地震因震中烈度比同等震级的其它震例偏高许多,而且多个台站均记录到长周期振动规则的正弦形面波而特别引人注目。精确测定了这组地震的震源位置,得到震源深度约等于１ｋｍ;对比分析了震相记录特征、震区周围的历史地震活动及地质构造背景,认为这是一组罕见的低震级高烈度震例,其发生可能与震中附近的Ｆ７断层活动有关。 相似文献
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Moment magnitudes of two large Turkish earthquakes on February 6, 2023 from long-period coda 
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下载免费PDF全文 Two large earthquakes (an earthquake doublet) occurred in south-central Turkey on February 6, 2023, causing massive damages and casualties. The magnitudes and the relative sizes of the two mainshocks are essential information for scientific research and public awareness. There are obvious discrepancies among the results that have been reported so far, which may be revised and updated later. Here we applied a novel and reliable long-period coda moment magnitude method to the two large earthquakes. The moment magnitudes (with one standard error) are 7.95±0.013 and 7.86±0.012, respectively, which are larger than all the previous reports. The first mainshock, which matches the largest recorded earthquakes in the Turkish history, is slightly larger than the second one by 0.11±0.035 in magnitude or by 0.04 to 0.18 at 95% confidence level. 相似文献
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HOLOCENE PALAEOSEISMOLOGIC RECORD AND RUPTURE BEHAVIOR OF LARGE EARTHQUAKES ON THE XIANSHUIHE FAULT 下载免费PDF全文
下载免费PDF全文 LI Dong-yu CHEN Li-chun LIANG Ming-jian GAO Shuai-po ZENG Di WANG Hu LI Yan-bao 《地震地质》2017,39(4):623-643
The Xianshuihe Fault, the boundary of Bayan Har active tectonic block and Sichuan-Yunnan active tectonic block, is one of the most active fault zones in the world. In the past nearly 300 years, 9 historical earthquakes of magnitude ≥ 7 have been recorded. Since 2008, several catastrophic earthquakes, such as Wenchuan MS8 earthquake, Yushu MS7.1 earthquake and Lushan MS7 earthquake, have occurred on the other Bayan Har block boundary fault zones. However, only the Kangding MS6.3 earthquake in 2014 was documented on the Xianshuihe Fault. Thus, the study of surface deformation and rupture behavior of large earthquakes in the late Quaternary on the Xianshuihe Fault is of fundamental importance for understanding the future seismic risk of this fault, and even the entire western Sichuan region. On the basis of the former work, combined with our detailed geomorphic and geological survey, we excavated a combined trench on the Qianning segment of Xianshuihe fault zone which has a long elapse time. Charcoal and woods in the trench are abundant. 30 samples were dated to constrain the ages of the paleoseismic events. Five events were identified in the past 9 000 years, whose ages are:8070-6395 BC, 5445-5125 BC, 4355-4180 BC, 625-1240 AD and the Qianning earthquake in 1893. The large earthquake recurrence behavior on this segment does not follow the characteristic earthquake recurrence model. The recurrence interval is 1000~2000 years in early period and in turn there is a quiet period of about 5 000 years after 4355-4180 BC event. Then it enters the active period again. Two earthquakes with surface rupture occurred in the past 1000 years and the latest two earthquakes may have lower magnitude. The left-lateral coseismic displacement of the 1893 Qianning earthquake is about 2.9m. 相似文献
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The source mechanism of a large (Ms ? 7.2) earthquake that occurred in the oceanic plate at the junction of the Tonga—Kermadec trench systems with the aseismic Louisville ridge is found by inverting long-period vertical-component Rayleigh waves recorded by the IDA network. The solution is an almost-pure normal fault, on a plane striking roughly parallel to the trench axis, with seismic moment of 1.7 × 1027 dyn cm, and thus is among the ten largest documented shallow normal-fault earthquakes. A point-source depth of 20 km for the event is resolved by modeling teleseismic body waves; the actual rupture may have extended deeper, to 30 or 40 km. The earthquake was a multiple event, consisting of two sources separated by 16 s. A rupture velocity of 3.5 km s?1 is inferred. The earthquake can be interpreted as tensional failure in the shallow portion of the downgoing plate caused by the gravitational pull of the slab. The Louisville ridge may be creating a local degree of decoupling of the oceanic plate from the overriding plate, and/or a zone of extension within the slab, which could enhance the effect of the gravitational forces in the shallower part of the downgoing plate. In particular, the earthquake could be associated with the break-up of the leading seamount of the ridge, which is currently right at the trench. Alternatively, the earthquake may have been caused by stresses associated with the bending of the plate prior to subduction. 相似文献
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The source process of the deep-focus Spanish earthquake of March 29, 1954 (mb = 7.1, h = 630 km) has been studied by using seismograms recorded at teleseismic distances. Because of its unusual location, this earthquake is considered to be one of the most important earthquakes that merit detailed studies. Long-period body-wave records reveal that the earthquake is a complicated multiple event whose wave form is quite different from that of usual deep earthquakes. The total duration of P phases at teleseismic distances is as long as 40 s. This long duration may explain the considerable property damage in Granada and Malaga, Spain, which is rather rare for deep earthquakes. Using the azimuthal distribution of the differences between the arrival times of the first, the second and later P phases, the hypocenters of the later events are determined with respect to the first event. The focus of the second event is located on the vertical nodal plane of the first shock suggesting that this vertical plane is the fault plane. This fault plane which strikes in N2°E and dips 89.1°E defines a nearly vertical dip-slip fault, the block to the west moving downwards. The time interval and spatial separation between the first and the second events are 4.3 s and 19 km respectively, giving an apparent rupture velocity of 4.3 km/s which is about 74% of the S-wave velocity at the source. A third event occurred about 8.8 s after the first event and about 35.6 km from it. At least six to ten events can be identified during the whole sequence. The mechanism of some of the later events, however, seems to differ from the first two events. Synthetic seismograms are generated by superposition of a number of point sources and are matched with the observed signals to determine the seismic moment. The seismic moments of the later events are comparable to, or even larger than, that of the first. The total seismic moment is determined to be 7 · 1027 dyn cm while the moments of the first and the second shocks are 2.1 · 1026 dyn cm and 5.1 · 1026 dyn cm, respectively. The earthquake may represent a series of fractures in a detached piece of the lithosphere which sank rapidly into the deep mantle preserving the heterogeneity of material property at shallow depths. 相似文献
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We present results from a detailed analysis of seismic and infrasonic data recorded over a four day period prior to the Vulcanian eruptive event at Sakurajima volcano on May 19, 1998. Nearly one hundred seismic and infrasonic events were recorded on at least one of the nine seismic–infrasonic stations located within 3 km of the crater. Four unique seismic event types are recognized based on the spectral features of seismograms, including weak seismic tremor characterized by a 5–6 Hz peak mode that later shifted to 4–5 Hz. Long-period events are characterized by a short-duration, wide spectral band signal with an emergent, high-frequency onset followed by a wave coda lasting 15–20 s and a fundamental mode of 4.2–4.4 Hz. Values of Q for long-period events range between 10 and 22 suggesting that a gas-rich fluid was involved. Explosive events are the third seismic type, characterized by a narrow spectral band signal with an impulsive high-frequency onset followed by a 20–30 second wave coda and a peak mode of 4.0–4.4 Hz. Volcano-tectonic earthquakes are the fourth seismic type. Prior to May 19, 1998, only the tremor and explosion seismic events are found to have an infrasonic component. Like seismic tremor, infrasonic tremor is typically observed as a weak background signal. Explosive infrasonic events were recorded 10–15 s after the explosive seismic events and with audible explosions prior to May 19. On May 19, high-frequency impulsive infrasonic events occurred sporadically and as swarms within hours of the eruption. These infrasonic events are observed to be coincident with swarms of long-period seismic events. Video coverage during the seismic–infrasonic experiment recorded intermittent releases of gases and ash during times when seismic and acoustic events were recorded. The sequence of seismic and infrasonic events is interpreted as representing a gas-rich fluid moving through a series of cracks and conduits beneath the active summit crater. 相似文献
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Seismic coda wave is the tail portion of the earthquake record after main arrivals. Studies on the coda usually focus on high-frequency data within several hours after regional events and attribute them to the scattering effect of the heterogeneities inside the earth. Here, we use records of seven large earthquakes at globally distributed seismic stations to examine the decay of long-period (100 s to 300 s) coda in the time window of 10,000 s to 140,000 s after the origin time and fit it with a statistical model. The geometric spreading effect in the estimated initial energy and a location-independent equivalent attenuation coefficient indicate that the long-period coda energy is less affected by the heterogeneity-induced scattering effect than that of shorter-period coda. The coda energy can reach the earth's inner core and can be explained by a 1D earth model, making it more effective for constraining the global attenuation model. It also has the potential to determine the magnitudes of large earthquakes and to explore the interior of planetary bodies. 相似文献
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The 2018,Songyuan,Jilin M_S5. 7 earthquake occurred at the intersection of the FuyuZhaodong fault and the Second Songhua River fault. The moment magnitude of this earthquake is M_W5. 3,the centroid depth by the waveform fitting is 12 km,and it is a strike-slip type event. In this paper,with the seismic phase data provided by the China Earthquake Network, the double-difference location method is used to relocate the earthquake sequence,finally the relocation results of 60 earthquakes are obtained. The results show that the aftershock zone is about 4. 3km long and 3. 1km wide,which is distributed in the NE direction. The depth distribution of the seismic sequence is 9km-10 km. 1-2 days after the main shock,the aftershocks were scattered throughout the aftershock zone,and the largest aftershock occurred in the northeastern part of the aftershock zone. After 3-8 days,the aftershocks mainly occurred in the southwestern part of the aftershock zone. The profile distribution of the earthquake sequence shows that the fault plane dips to the southeast with the dip angle of about 75°. Combined with the regional tectonic setting,focal mechanism solution and intensity distribution,we conclude that the concealed fault of the Fuyu-Zhaodong fault is the seismogenic fault of the Songyuan M_S5. 7 earthquake. This paper also relocates the earthquake sequence of the previous magnitude 5. 0 earthquake in 2017. Combined with the results of the focal mechanism solution,we believe that the two earthquakes have the same seismogenic structure,and the earthquake sequence generally develops to the southwest. The historical seismic activity since 2009 shows that after the magnitude 5. 0 earthquake in 2017,the frequency and intensity of earthquakes in the earthquake zone are obviously enhanced,and attention should be paid to the development of seismic activity in the southwest direction of the earthquake zone. 相似文献
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基于Aki等（1975）的地方震尾波单次散射模型,利用文山地震台记录到2005年8月13日在云南文山县发生的5.3级地震余震序列的数字化波形观测资料,测量了震源区尾波Q（f）值。测量结果表明,当中心频率为1．5Hz时,文山地区的尾波Q值在52～155之间,平均值为91,尾波的振幅衰减率β（f）在0.013～0．039之间,平均值为0．024;测量得到该区尾波Qc值与频率f的关系为Qc（f）=62f^“0.87;尾波波源因子A0与震级ML成正比关系,满足关系lgA0=1．02ML-0．73。此次地震的发震构造为文山断裂带,地震波受到破碎带强烈的非弹性吸收,尾波Qc值明显降低。 相似文献
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Maximum earthquake size varies considerably amongst the subduction zones. This has been interpreted as a variation in the seismic coupling, which is presumably related to the mechanical conditions of the fault zone. The rupture process of a great earthquake indicates the distribution of strong (asperities) and weak regions of the fault. The rupture process of three great earthquakes (1963 Kurile Islands, MW = 8.5; 1965 Rat Islands, MW = 8.7; 1964 Alaska, MW = 9.2) are studied by using WWSSN stations in the core shadow zone. Diffraction around the core attenuates the P-wave amplitudes such that on-scale long-period P-waves are recorded. There are striking differences between the seismograms of the great earthquakes; the Alaskan earthquake has the largest amplitude and a very long-period nature, while the Kurile Islands earthquake appears to be a sequence of magnitude 7.5 events.The source time functions are deconvolved from the observed records. The Kurile Islands rupture process is characterized by the breaking of asperities with a length scale of 40–60 km, and for the Alaskan earthquake the dominant length scale in the epicentral region is 140–200 km. The variation of length scale and MW suggests that larger asperities cause larger earthquakes. The source time function of the 1979 Colombia earthquake (MW = 8.3) is also deconvolved. This earthquake is characterized by a single asperity of length scale 100–120 km, which is consistent with the above pattern, as the Colombia subduction zone was previously ruptured by a great (MW = 8.8) earthquake in 1906.The main result is that maximum earthquake size is related to the asperity distribution on the fault. The subduction zones with the largest earthquakes have very large asperities (e.g. the Alaskan earthquake), while the zones with the smaller great earthquakes (e.g. Kurile Islands) have smaller scattered asperities. 相似文献