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1.
中国是世界上地震多发的地区之一。在各省份中,处于中国西南部的云南省是地震发生最多的省份之一。云南省省会昆明以南60 km处的抚仙湖位于小江地震带和通海-石屏地震带的交汇处,该地区的地震频次又居云南省之首。如果能在抚仙湖的沉积物中找到历史地震的自然记录并解释其机理,就意味着发现了一个由抚仙湖自然形成的地震记录仪。提供了证明抚仙湖区域历史地震自然记录存在的证据---抚仙湖沉积物的磁化率。我们在抚仙湖的中心地带、水深108 m处,钻取到了170 cm长的抚仙湖沉积物剖面,经测试证明它对应着近1 000年,约公元1025年至今的沉积年代。在研究中,沉积物磁化率的峰值突变与过去1 000年中许多有历史记载的地震事件相吻合。此外,一些尚没有记载的古地震事件也通过对湖底沉积物磁化率的分析而得以发现。 相似文献
2.
At four sites in Turkey and Armenia the physico-chemical properties of thermal and mineral waters were monitored continuously
during the Izmit and Düzce earthquakes that occurred along the North Anatolian fault in August and November 1999. The epicentral
distances between the moment magnitude (Mw) 7.6 Izmit earthquake and the monitoring locations were 313, 488, 1,161, and 1,395 km. At the most distant site, the specific
electrical conductivity of mineral water from a flowing artesian well dropped co-seismically and postseismically by 7%. No
changes were observed at the other sites, although the estimated earthquake strains and peak ground accelerations are much
higher. A similar pattern was observed after the Düzce earthquake, which happened three months after the Izmit event. The
response of a hydrogeological system seems to depend on the site characteristics rather than on the nature of the earthquake.
A hydrogeological model for the sensitive observation site farthest from the Izmit earthquake explains the observations in
terms of a changed mixing ratio between two fluid components. Passing seismic waves may trigger a local pore-pressure increase
according to the mechanism of advective overpressure. The preconditions for this mechanism, free gas bubbles in the aquifer
in combination with a trap for rising bubbles, is probably not fulfilled by the other groundwater systems.
Electronic Publication 相似文献
3.
《Sedimentology》2018,65(5):1777-1799
Sequences of lake sediments often form long and continuous records that may be sensitive recorders of seismic shaking. A multi‐proxy analysis of Lake Bohinj sediments associated with a well‐constrained chronology was conducted to reconstruct Holocene seismic activity in the Julian Alps (Slovenia). A seismic reflection survey and sedimentological analyses identified 29 homogenite‐type deposits related to mass‐wasting deposits. The most recent homogenites can be linked to historical regional earthquakes (i.e. 1348 ad , 1511 ad and 1690 ad ) with strong epicentral intensity [greater than ‘damaging’ (VIII ) on the Medvedev–Sponheuer–Karnik scale]. The correlation between the historical earthquake data set and the homogenites identified in a core isolated from local stream inputs, allows interpretation of all similar deposits as earthquake related. This work extends the earthquake chronicle of the last 6600 years in this area with a total of 29 events recorded. The early Holocene sedimentary record is disturbed by a seismic event (6617 ± 94 cal yr bp ) that reworked previously deposited sediment and led to a thick sediment deposit identified in the seismic survey. The period between 3500 cal yr bp and 2000 cal yr bp is characterized by a major destabilization in the watershed by human activities that led to increases in erosion and sedimentation rates. This change increased the lake's sensitivity to recording an earthquake (earthquake‐sensitivity threshold index) with the occurrence of 72 turbidite‐type deposits over this period. The high turbidite frequency identified could be the consequence of this change in lake earthquake sensitivity and thus these turbidites could be triggered by earthquake shaking, as other origins are discarded. This study illustrates why it is not acceptable to propose a return period for seismic activity recorded in lake sediment if the sedimentation rate varies significantly. 相似文献
4.
《International Geology Review》2012,54(9):876-882
The active North Anatolian fault zone (NAFZ) presents very complex seismotectonic activity. The occurrence of the Abant earthquake in 1957 (Ms = 7.1) and the Mudurnu earthquake in 1967 (Ms = 6.8) are only two examples of several seismic events associated with intense tectonic activity of the NAFZ. Statistical analyses of earthquakes in an area extending between 30° 30′ to 31° 30' E Long. and 40° 15′ to 41° 00′ N Lat. reveal that epicenters generally were shallow. However, a few deep epicenters also were located, some of which reached a depth of 30 km. The epicenters were found to concentrate in a zone lying between the Duzce and Akyazi Plain to the north of Almacik Mountain and in the Adapazari Plain. The Northern Anatolian fault displays an en echelon character in the area, except for the eastern part, where it extends as a single segment. The en echelon character of the NAFZ is interpreted as a structure distributing the potential energy and consequently reducing the intensity of earthquakes, giving rise to micro-earthquakes of magnitudes less than 4.2. 相似文献
5.
岱海位于半干旱区东部边缘及东亚夏季风的尾闾区，生态环境体系脆弱，气候和环境变化敏感，是研究环境变化的理想地区。65个湖泊表层及入湖河流冲积物样品的孢粉分析揭示了岱海表层孢粉沉积特征及孢粉来源。岱海表层孢粉主要来源于区域性植被的孢粉，其总体特征反映了区域植被的组成，但不同部位孢粉组合的差异反映了湖滨当地植被的变化。受沉积环境的影响，岱海湖区孢粉浓度总体上要低于入湖河流孢粉浓度，湖区中部孢粉浓度最高。岱海孢粉以河流携带的为主，同时受风力传播的影响。蒿、藜科、桦、虎榛子等花粉和蕨类孢子以河流搬运的为主，松、禾本科及莎草科花粉可能还受风力传播的影响。一些仅在个别样品中出现且百分比很低的花粉类型如豆科、十字花科等还有可能是昆虫、鸟类或人类活动携带而来。 相似文献
6.
This work focuses on the use of electromagnetic emissions (EM) in the HF band as a warning event for earthquakes. EM at HF components 41 MHz and 46 MHz were monitored and recorded from eight field stations in Greece and correlated with seismological events. Directivity effect raised since EM emissions at specific station locations were correlated to earthquake events from prescribed regions. EM recordings during 1999 were used and by visual inspection were associated to most of the earthquake events greater than 5R. Using these observations a novel algorithm based on the ratio of short term to long term signal average, together with a prediction rules set derived from 1999's EM emissions study were developed to combine results from several field stations. Performance of the system was promising, but was dependent on the geographic area of interest. Overall performance for earthquakes events of magnitude greater than 5.7 R was 75% of seismic events were correctly predicted by EM activity, while 25% were not predicted. 相似文献
7.
Earthquake-induced deformation structures in lake deposits: A Late Pleistocene to Holocene paleoseismic record for Central Switzerland 总被引：1，自引：0，他引：1
Katrin Monecke Flavio S. Anselmetti Arnfried Becker Michael Schnellmann Michael Sturm Domenico Giardini 《Eclogae Geologicae Helvetiae》2006,99(3):343-362
8.
We investigate spatial clustering of 2414 aftershocks along the Izmit Mw = 7.4 August 17, 1999 earthquake rupture zone. 25 days prior to the Düzce earthquake Mw = 7.2 (November 12, 1999), we analyze two spatial clusters, namely Sakarya (SC) and Karadere–Düzce (KDC). We determine the earthquake frequency–magnitude distribution (b-value) for both clusters. We find two high b-value zones in SC and one high b-value zone in KDC which are in agreement with large coseismic surface displacements along the Izmit rupture. The b-values are significantly lower at the eastern end of the Izmit rupture where the Düzce mainshock occurred. These low b-values at depth are correlated with low postseismic slip rate and positive Coloumb stress change along KDC. Since low b-values are hypothesized with high stress levels, we propose that at the depth of the Düzce hypocenter (12.5 km), earthquakes are triggered at higher stresses compared to shallower crustal earthquake. The decrease in b-value from the Karadere segment towards the Düzce Basin supports this low b-value high stress hypothesis at the eastern end of the Izmit rupture. Consequently, we detect three asperity regions which are correlated with high b-value zones along the Izmit rupture. According to aftershock distribution the half of the Düzce fault segment was active before the 12 November 1999 Düzce mainshock. This part is correlated with low b-values which mean high stress concentration in the Düzce Basin. This high density aftershock activity presumably helped to trigger the Düzce event (Mw = 7.2) after the Izmit Mw 7.4 mainshock. 相似文献
9.
A multiarchive approach has been applied to the investigation of the late Pleistocene and Holocene record of strong earthquakes in Switzerland. The geological archives used for this study include active faults, lake deposits, slope instabilities, and caves. In the Basle area, eight trenches were opened across the Basle–Reinach fault, nearby rockfall deposits were systematically investigated, sediment cores were taken from two lakes, and nine caves were studied. In Central Switzerland, five lakes were investigated by means of high-resolution seismic lines and sediment cores. Furthermore, three caves were studied in Central Switzerland. Altogether, the investigations are based on more than 350 km of high-resolution reflection seismic lines, 450 m of core samples, 260 m of trenches, and 245 radiocarbon age determinations. The measured co-seismic displacements along the Basle–Reinach fault supply independent information for the magnitude of the AD 1356 Basle earthquake exclusively based on geological evidence. Deformation features related to three well-documented strong historic earthquake shocks were identified. Deformation features of the AD 1774 Altdorf and AD 1601 Unterwalden earthquakes can be used to calibrate paleoseismic evidence in Central Switzerland. Altogether, traces of 13 earthquakes could be found in the two study areas, all of them with magnitudes Mw 6 or greater. For the first time, the earthquake catalogue for Switzerland can be extended back beyond historic records, into the late Pleistocene, spanning 15,000 years. 相似文献
10.
受环太平洋地震带影响,华北平原地区地震频发,尤其是处于中国首都经济圈的京津冀地区的地震事件备受关注。通过对历史文献资料及地震台网记录中的地震事件统计、分析,重建该地区地震事件历史并获取其潜在的空间分布特征及时间规律,对未来地震事件的早期预警具有重要参考意义。分析结果表明,公元前231年至公元2018年期间京津冀地区发生的1044起地震事件中,以有感地震和中强地震为主,小地震、强烈地震以及大地震发生频次较低。地震记录完整性分析结果表明,除小地震外,其他等级地震记录自公元1400年以来基本完整。在空间分布上,京津冀地区历史地震呈“T”字形分布,沿1条北西—南东走向地震带和1条北东—南西走向地震带分布。在时间上,京津冀地区地震事件呈现出阶段性的变化,在公元1480—1680年间以及1950年以来2个时间段内较为活跃,发生频率较高,频谱分析结果进一步表明地震记录存在45年的复发周期。在月际尺度上,地震事件同样存在季节性差异且多发于夏秋季节,同时地震密集区域在年内呈现出自西向东迁移的现象。最后,根据历史地震事件发生的时间规律,在未来一段时间内京津冀地区仍将处于地震活跃期,存在发生强震的风险。 相似文献
11.
Elke Vandekerkhove Maarten Van Daele Nore Praet Veerle Cnudde Peter J. Haeussler Marc De Batist 《Sedimentology》2020,67(1):364-389
Lake sediments in Eklutna Lake, Alaska, reveal the presence of turbidites within varved sequences. These turbidites, which result from flood events and earthquakes, show a similar macroscopic appearance. In order to use turbidites to reconstruct flood variability and/or seismic history in the lake basin, it is crucial to determine the trigger of the turbidity currents. This study examined the turbidite caused by the ad 1964 Great Alaska earthquake as well as turbidites linked to historical flood events in order to differentiate between these earthquake-triggered and flood-triggered turbidites. In a suite of samples from throughout the lake, distinctive proxies are identified that can be associated with event-specific flow characteristics. The study presents straightforward discrimination methods related to the sedimentology and geochemical components of the turbidites. These methods are also applicable to other lakes, particularly proglacial lakes where the sediment composition of onshore and offshore sources is similar. Finally, the discrimination of the turbidite trigger can be used to reconstruct the palaeoflood and seismic history. 相似文献
12.
The advent of high-resolution digital seismic recording and advances in computer technology enable the combination of traditional regional seismic network observations with direct seismogram modeling to improve estimates of small earthquake faulting geometry, depth, and size. We illustrate a combined modeling approach using observations from three earthquakes that occurred within the environs of the New Madrid Seismic Zone: two Missouri earthquakes from September 26, 1990 and May 4, 1991; and the southern Illinois earthquake of February 5, 1994. We also re-examine the faulting geometry for two events from the 1960s that are inconsistent with the current estimate of the regional stress field. Based on direct modeling of the long-period seismograms associated with these events, we revise earlier estimates of the earthquake parameters for the March 3, 1963 and July 21, 1967 Missouri earthquakes. Comparing the new and revised results with existing earthquake mechanisms in the region, we find that tension-axes are generally aligned in a N-S to NW-SE direction, while the compression-axes trend in a NE to E direction. An interesting exception to this pattern are the March 3, 1963 and two nearby earthquakes that lie within a well-defined 30-km long left step in seismicity near New Madrid. 相似文献
13.
Increasing sediment loads entering the Lake Tanganyika ecosystem are hastening the need for improved understanding of the linkages between catchment characteristics and influent sediment transport and loading. Sediment loads of two catchments at the southern end of the lake were estimated for October 1998–December 1999, and catchment characteristics determined using GIS. It was found that both sediment yields and loads were higher from the catchment of the Lunzua River (19.8 t km?2 and 20,114 t, respectively) compared with that of the Kalambo (4.1 t km?2 and 12,197 t) in 1999. These differences were both attributed to the smaller size and higher road density of the Lunzua catchment, and suggest that previous recommendations regarding the positioning of underwater lake reserves fail to take into account the low sediment retention capacity of small mountainous rivers. Differences between the study rivers in the transport of suspended sediments, organic matter, and bedload sediments into the lake were also found, the latter determined by the novel application of the 'McLaren Model'. 相似文献
14.
Nore Praet Maarten Van Daele Tim Collart Jasper Moernaut Elke Vandekerkhove Philipp Kempf Peter J. Haeussler Marc De Batist 《Sedimentology》2020,67(5):2332-2359
Turbidites embedded in lacustrine sediment sequences are commonly used to reconstruct regional flood or earthquake histories. A critical step for this method to be successful is that turbidites and their trigger mechanisms are determined unambiguously. The latter is particularly challenging for prehistoric proglacial lake records in high-seismicity settings where both earthquake-generated and flood-generated turbidites interrupt the background varved sedimentation. This calls for a new method to allow efficient and objective identification and classification of turbidites. This study examined turbidites in five long (9 to 17 m) sediment cores from Eklutna Lake, a proglacial lake in south-central Alaska, using standard core logging and grain-size data. A novel statistical approach is presented, in which varve-thickness distributions were first analyzed to objectively identify the thickest turbidites and distinguish them from background sedimentation. For each turbidite, a selection of variables were then measured, including: basal grain-size, thickness, magnetic susceptibility and spectrophotometric variables. Triggering mechanisms were discriminated by a combination of principal component analysis and clustering, and by calibration with historical events. Using this approach, a 2250 year long lake-wide event stratigraphy was constructed, with 94 prehistoric events, including 24 earthquake and 70 flood events. Basal grain-size and thickness variables turn out to be the most effective proxies for discrimination. This statistical approach is a powerful and new method to identify turbidites and their triggering mechanisms in long prehistoric sediment records. It opens up new prospects for palaeoseismological, palaeohydrological and palaeoclimate studies in proglacial lakes worldwide. 相似文献
15.
We present a preliminary study of strong ground motion during the largest aftershock (Mw 5.8) of the 1999 Izmit earthquake (Mw 7.4), Turkey, at 11:55 on 13 September 1999. The peak ground acceleration observed near the epicentre of this aftershock was in agreement with that predicted by standard empirical prediction equations. Its spectral source parameters of the largest aftershock are also typical for a Mw 5.8 earthquake. At greater epicentral distances, there is an order-of-magnitude in scatter in peak ground acceleration values for this aftershock, which is attributed to site effects. The presence of thick layers of low-velocity sediments caused significant amplification of S-waves in the Avcılar district of Istanbul, at frequencies of 1 Hz, explaining the observed concentration of damage there as a result of the Izmit mainshock. 相似文献
16.
The study area, just to the west of the Verrill Canyon on the Scotian Slope, eastern Canada, exhibits both large and small scale sediment mass movement features. Study of high resolution seismic reflection and sidescan sonar data shows that a large portion (approximately 70%) of the near surface sediment (<20 m) in the area has undergone erosion, rotational slumping and internal deformation. Remoulded sediment observed in physical properties profiles of piston cores and sediment deformation structures are further evidence of slumping. Small scale mass flow events are recorded by abundant turbidites and debris flow deposits noted in piston cores. Sediment physical properties are highly dependent on sediment type (lithofacies). Frequent facies changes, both temporally and spatially, make correlation between cores difficult. Although the small scale mass movement events correlate with glacial recession on the continental shelf and lower relative sea levels, the triggering mechanisms for the large scale events are less obvious. Slope stability analyses indicate that, at present, the seabed is stable. The most plausible explanation for large scale slope failures in this region are ground accelerations related to earthquake shock. Our analyses demonstrate that it is unlikely that large magnitude, distant earthquakes, such as those previously proposed in the Laurentian Slope Seismic Zone (LSP) model, could initiate failure of sediment in the study region. Our data support the interpretation that more frequent, lower magnitude earthquakes, closer to the study region, as previously proposed in the Eastern Slope Experimental Source Zone (ESX) model, are the likely causes of large scale slope failures. Furthermore, excess pore pressures resulting from shallow gas and/or high sedimentation rates during deglaciation contribute to slope failure. 相似文献
17.
Use of tsunami waveforms for earthquake source study 总被引：1，自引：0，他引：1
Tsunami waveforms recorded on tide gauges, like seismic waves recorded on seismograms, can be used to study earthquake source processes. The tsunami propagation can be accurately evaluated, since bathymetry is much better known than seismic velocity structure in the Earth. Using waveform inversion techniques, we can estimate the spatial distribution of coseismic slip on the fault plane from tsunami waveforms. This method has been applied to several earthquakes around Japan. Two recent earthquakes, the 1968 Tokachi-oki and 1983 Japan Sea earthquakes, are examined for calibration purposes. Both events show nonuniform slip distributions very similar to those obtained from seismic wave analyses. The use of tsunami waveforms is more useful for the study of unusual or old earthquakes. The 1984 Torishima earthquake caused unusually large tsunamis for its earthquake size. Waveform modeling of this event shows that part of the abnormal size of this tsunami is due to the propagation effect along the shallow ridge system. For old earthquakes, many tide gauge records exist with quality comparable to modern records, while there are only a few good quality seismic records. The 1944 Tonankai and 1946 Nankaido earthquakes are examined as examples of old events, and slip distributions are obtained. Such estimates are possible only using tsunami records. Since tide-gauge records are available as far back as the 1850s, use of them will provide unique and important information on long-term global seismicity. 相似文献
18.
岷江上游新磨村湖相沉积物粒度端元反演及其记录的构造和气候事件 总被引：1，自引：0，他引：1
应用沉积物粒度端元分析模型对岷江上游新磨村湖相沉积高分辨率粒度数据序列进行了反演,分离出2个端元。根据端元的频率分布曲线和沉积学分析,并结合岷江上游的地质构造背景,分析了各端元与研究区物源和古地震活动的对应关系。EM1为震间期的湖泊沉积,代表风力近源搬运的极细颗粒组分;EM2为极端灾变(地震等)期间的湖泊沉积,代表风力为主和部分水力近距离搬运的细颗粒组分。对新磨村剖面分离出的EM2百分含量与中值粒径、20~63μm、63~200μm粒径组分、磁化率值及地球化学比值(SiO2/Al2O3、TiO2/Al2O3、CaO/Al2O3、Sr/Al2O3、Rb/Sr,Na2O/Al2O3)进行对比分析,各指标的突变明显受粒度变化控制,指示可能的地震事件,进而识别出26次地震事件。为确定地震事件所代表的地震震级,基于震级与累积砂层厚度关系进行估算,共获得16次5~6级,5次6~7级,5次>7级地震。因此,采用粒度端元模拟不仅可以分离出不同的粒径组分和各组分百分含量,有效识别出不同动力组分和沉积动力环境,还可以较好地厘定出沉积记录的构造事件(地震等)等,更好地理解构造活动在地质、地貌演化中的作用。 相似文献
19.
内蒙古东乌珠穆沁旗西山巴润特花组孢型化石及其时代 总被引：1，自引：0，他引：1
高联达 《华北地质矿产杂志》1996,11(1):24-30,T002
本文首次报道内蒙古东乌珠穆沁旗西山下泥盆统巴润特花组底部所发现的丰富的孢型石。共发现孢子１８属，３９种，其中新种２个；凝类４属５种，通过孢型化石的研究，确定巴润特花组为早泥盆世早期，相当西欧吉丁阶，并可与中国云南东部，四川龙门山，西秦岭和新疆西准噶尔同时期孢带比较。 相似文献
20.
Shan-Chieh Chuang Hongey Chen Guan-Wei Lin Ching-Weei Lin Chung-Pai Chang 《Engineering Geology》2009,103(1-2):59-65
The landslide area along the Tachia River catchment of central Taiwan was investigated using the remote sensing images of various typhoon and earthquake events taken from 1996 to 2004 and the sediment discharge measured at hydrometric stations. Our findings indicate that 88% of the coseismic landslides triggered by the 1999 Chi-Chi earthquake were first-time occurrences. After the Chi-Chi earthquake, 59% of the landslide area was reactivated during typhoon Toraji and 66% during typhoon Mindulle. The landslides prone to reactivation were on the formations with closely spaced discontinuities. It is suggested that further rock-mass defects in the formations were added or opened by the earthquake, and that the landslide areas continued to extend until the end of 2004. Post-1999 rainstorms delivered large amounts of colluvial sediment into the main channel, leading to a 2-fold increase in post-seismic sediment discharge while the precipitation was only half that of the pre-earthquake rate. 相似文献