2022年9月5日四川泸定MS6.8地震舆情分析

2022年9月5日12时52分,四川省甘孜州泸定县发生 M_S6.8地震,造成重大人员伤亡,引起社会公众的广泛关注。突发事件的信息发布和舆情引导越来越受到党和政府的高度重视,相关信息公开效率的影响甚至决定了事件处置的舆情发展。本研究以中国地震台网中心为舆情引导主体,对四川泸定 M_S6.8地震舆情进行分析研究,总结舆情引导经验,探讨突发地震舆情引导对地震部门有效开展震后应急的促进作用,以期为今后的防震减灾新闻宣传工作带来启示和思考。     

The initial subevent of the 1994 Northridge, California, earthquake: Is earthquake size predictable?

We examine the initial subevent (ISE) of the M 6.7, 1994 Northridge, California, earthquake in order to discriminate between two end-member rupture initiation models: the preslip and cascade models. Final earthquake size may be predictable from an ISE's seismic signature in the preslip model but not in the cascade model. In the cascade model ISEs are simply small earthquakes that can be described as purely dynamic ruptures. In this model a large earthquake is triggered by smaller earthquakes; there is no size scaling between triggering and triggered events and a variety of stress transfer mechanisms are possible. Alternatively, in the preslip model, a large earthquake nucleates as an aseismically slipping patch in which the patch dimension grows and scales with the earthquake's ultimate size; the byproduct of this loading process is the ISE. In this model, the duration of the ISE signal scales with the ultimate size of the earthquake, suggesting that nucleation and earthquake size are determined by a more predictable, measurable, and organized process. To distinguish between these two end-member models we use short period seismograms recorded by the Southern California Seismic Network. We address questions regarding the similarity in hypocenter locations and focal mechanisms of the ISE and the mainshock. We also compare the ISE's waveform characteristics to those of small earthquakes and to the beginnings of earthquakes with a range of magnitudes. We find that the focal mechanisms of the ISE and mainshock are indistinguishable, and both events may have nucleated on and ruptured the same fault plane. These results satisfy the requirements for both models and thus do not discriminate between them. However, further tests show the ISE's waveform characteristics are similar to those of typical small earthquakes in the vicinity and more importantly, do not scale with the mainshock magnitude. These results are more consistent with the cascade model.     

2022年9月5日四川泸定MS6.8地震序列重定位研究

利用2022年9月5—12日震相报告中的P波和S波到时资料,采用双差定位方法对四川泸定M_S6.8地震序列的主震和余震进行重定位。重新定位后地震序列较重新定位之前震中分布更加集中,线性趋势更加明显。余震主要分布在鲜水河断裂以西地区,总体沿着鲜水河断裂呈NW向展布,余震区长轴约为65km。根据重定位结果,发震断层为鲜水河断裂磨西—石棉段,该断裂走向为331°～340°,倾角较陡。受SW向海螺沟段断裂影响,余震区具有明显的分段特征,总体上呈现北浅南深的特征。随时间的演化,余震区中南段震源深度逐渐变浅,且地震频次逐渐衰减,而北段震源深度变化不大,频次也未明显减弱。不同时段的余震活动表明,本次地震的初始破裂方向为SE向,该破裂随后触发了与主断裂共轭的SW向分支断裂,余震沿这两个方向逐步扩展,最后达到稳定状态。     

Rapid report of the 8 January 2022 ​MS 6.9 Menyuan earthquake,Qinghai, China

The M_S 6.9 Menyuan earthquake in Qinghai Province, west China is the largest earthquake by far in 2022. The earthquake occurs in a tectonically active region, with a background b-value of 0.87 within 100 ?km of the epicenter that we derived from the unified catalog produced by China Earthquake Networks Center since late 2008. Field surveys have revealed surface ruptures extending 22 ?km along strike, with a maximum ground displacement of 2.1 ?m. We construct a finite fault model with constraints from InSAR observations, which showed multiple fault segments during the Menyuan earthquake. The major slip asperity is confined within 10 ?km at depth, with the maximum slip of 3.5 ?m. Near real-time back-projection results of coseismic radiation indicate a northwest propagating rupture that lasted for ～10 ?s. Intensity estimates from the back-projection results show up to a Mercalli scale of IX near the ruptured area, consistent with instrumental measurements and the observations from the field surveys. Aftershock locations (up to January 21, 2022) exhibit two segments, extending to ～20 ?km in depth. The largest one reaches M_S 5.3, locating near the eastern end of the aftershock zone. Although the location and the approximate magnitude of the mainshock had been indicated by previous studies based on paleoearthquake records and seismic gap, as well as estimated stressing rate on faults, significant surface-breaching rupture leads to severe damage of the high-speed railway system, which poses a challenge in accurately assessing earthquake hazards and risks, and thus demands further investigations of the rupture behaviors for crustal earthquakes.     

How deep was the Dudley (UK) earthquake of 22 September 2002?

On 22 September 2002, the largest UK earthquake (m_b4.3) of the last 10 years occurred near the town of Dudley in the West Midlands. Here we determine the earthquake focal mechanism and depth using data from stations at regional and teleseismic distances. Short-period teleseismic seismograms are interpreted in terms of P and surface reflections pP and sP. This analysis suggests that the source depth is deeper than the 9.7 km initially determined by the British Geological Survey (BGS). The relative amplitude method is applied to four teleseismic seismograms to support our interpretation of the surface reflections, and constrain the focal mechanism. Our preferred focal mechanism, a near vertical strike-slip with _s = 94°, = 88° and = –179°, is in reasonable agreement with a moment tensor determined by the Swiss Seismological Service. Synthetic regional surface wave seismograms match the observed seismograms for a model focal depth of 19.5 (±3.0) km and scalar moment, M₀, of 3.2 × 10¹⁵ N m. Our results emphasize that due to the well-known trade-off between depth and M₀ from inversions of long period (0.02–0.1 Hz) surface waves, it is preferable to combine long- and short-period data to constrain reliably the depth and hence estimate M₀. Our focal mechanism and depth are further validated by generating short-period synthetic seismograms that match the observations.     

2022年9月5日四川泸定MS6.8地震引起的水温同震响应特征分析

基于全国地下流体观测网的水温观测数据,分析2022年9月5日四川泸定 M_S6.8 地震引起的水温同震响应特征,并结合同震静态应变场探讨了水温同震响应机理。结果表明,泸定 M_S6.8 地震水温同震观测点主要分布在龙门山断裂带和川滇菱形块体中南部; 震中距Δ≤500km范围内水温同震以下降—恢复型和上升型为主,水温同震项数及测项比随震中距的增加逐渐减少; 水温同震响应幅度与震中距和地震能量密度显著相关,且随震中距的增加呈指数衰减,随地震能量密度的增加呈指数增大; 水温同震响应持续时间主要集中在1天以内,持续时间随震中距的增加呈指数衰减。     

Strong earthquake activity all over the world and strong-moderate earthquake activity within and near China (August, 1999～September, 1999)

Illustration All the data in this catalog are chosen from the "Preliminary Seismological Report of Chinese Seismic Stations" (Its abbreviation is "Monthly Report"). The catalog includes the events of M4.7 in and near China and M6 all over the world. The "Monthly Report" is monthly compiled by the Ninth Section of Institute of Geophysics, CSB.     

Strong earthquake activity all over the world and strong-moderate earthquake activity within and near China(August,1997～September,1997)

ＳｔｒｏｎｇｅａｒｔｈｑｕａｋｅａｃｔｉｖｉｔｙａｌｏｖｅｒｔｈｅｗｏｒｌｄａｎｄｓｔｒｏｎｇｍｏｄｅｒａｔｅｅａｒｔｈｑｕａｋｅａｃｔｉｖｉｔｙｗｉｔｈｉｎａｎｄｎｅａｒＣｈｉｎａ（Ａｕｇｕｓｔ,１９９７～Ｓｅｐｔｅｍｂｅｒ,１９９７）ＰＥＩ?..     

Strong earthquake activity all over the world and strong-moderate earthquake activity within and near China (August, 2000 ~ September, 2000)

IllustrationAll the data in this catalog are chosen from the (Preliminary Seismological Report of Chinese Seismic Stations( (Its abbreviation is (Monthly Report(). The catalog includes the events of M(4.7 in and near China and M(6 all over the world. The (Monthly Report( is monthly compiled by the Ninth Section of Institute of Geophysics, CSB.The origin times of earthquakes in the catalog adopt coordinated universal time (UTC) in accordance with international convention. The location…     

Strong earthquake activity all over the world and strong-moderate earthquake activity within and near China (August, 2004～September, 2004)

Illustration All the data in this catalog are chosen from the ″Preliminary Seismological Report of Chi-nese Seismic Stations″ (Its abbreviation is ″Monthly Report″). The catalog includes the events ofM≥4.7 in and near China and M≥6 all over the world. The ″Monthly Report″ is monthly compiledby the Ninth Section of Institute of Geophysics, China Earthquake Administration. The origin times of earthquakes in the catalog adopt coordinated universal time (UTC) inaccordan…     

Strong earthquake activity all over the world and strong-moderate earthquake activity within and near China (August, 2002 ~ September, 2002)

Illustration All the data in this catalog are chosen from the Preliminary Seismological Report of Chi-nese Seismic Stations (Its abbreviation is Monthly Report). The catalog includes the events of M4.7 in and near China and M6 all over the world. The Monthly Report is monthly compiled by the Ninth Section of Institute of Geophysics, CSB. The origin times of earthquakes in the catalog adopt coordinated universal time (UTC) in accordance with international convention. The location of e…     

Strong earthquake activity all over the world and strong-moderate earthquake activity within and near China (August, 1998 ～ September, 1998)

Illustration All the data in this catalogue are chosen from the ″Preliminary Seismological Report of Chinese Seismic Stations″ (Its abbreviation is ″Monthly Report″). The catalogue includes the events of M ≥ 4.7 in and near China and M ≥ 6 all over the world. The ″Monthly Report″ is monthly compiled by the Ninth Section of Institute of Geophysics, CSB.     

Strong earthquake activity all over the world and strong-moderate earthquake activity within and near China(September,1996～November,1996)

Ｓｔｒｏｎｇｅａｒｔｈｑｕａｋｅａｃｔｉｖｉｔｙａｌｏｖｅｒｔｈｅｗｏｒｌｄａｎｄｓｔｒｏｎｇ┐ｍｏｄｅｒａｔｅｅａｒｔｈｑｕａｋｅａｃｔｉｖｉｔｙｗｉｔｈｉｎａｎｄｎｅａｒＣｈｉｎａ（Ｓｅｐｔｅｍｂｅｒ，１９９６～Ｎｏｖｅｍｂｅｒ，１９９６）ＰＥＩ...     

Is clustered seismicity an indicator of regional stress? Insights from earthquake sequences in Yongning-Luguhu faulted basin,Southwest China

Using hypocenter relocation, moment tensor inversion, stress field inversion, and fault slip tendency analysis, this study systematically investigated three M5.5–5.8 earthquake sequences that occurred after 2000 in the Yongning-Luguhu faulted basin in the middle of the Lijiang-Xiaojinhe fault zone within the Sichuan-Yunnan block, Southwest China. Our results show that since the 2008 Wenchuan Earthquake, the tectonic stress pattern in this area may have changed and that b-values estimated for the earthquake sequences show evidence of an increasing trend in stress in the study area. Seismicity in the small-scale faulted basin adjacent to the large-scale fault zone is a possible indicator of regional stress. We also note that the aftershocks of the M5.7 earthquake sequence in 2012 and the M5.5 earthquake sequence in 2022 show relatively clear fluid diffusion-triggering characteristics. Overpressure of deep fluids is still the main factor driving seismic activity in the region, and we propose that the background tectonic stresses have not yet reached critical levels.     

Reports from the Smithsonian’s Global Volcanism Network,September 2008

Information included in this summary is based on more detailed reports published in the Bulletin of the Global Volcanism Network, vol. 33, no. 9, September 2008 (on the Internet at ). Edited by scientists at the Smithsonian, this bulletin includes reports provided by a worldwide network of correspondents. The reports contain the names and contact information for all sources. Please note that these reports are preliminary and subject to change as events are studied in more detail. The Global Volcanism Program welcomes further reports of current volcanism, seismic unrest, monitoring data, and field observations.     

Study on relationship between features of strain anomaly obtained by borehole strain meter at Wushi station in Xinjiang and strong earthquake: Taking Jiashi MS = 6.8 earthquake as an example

Introduction According to the Seismograph Network of China, an earthquake of MS=6.8 occurred at10:03:42 on February 24, 2003 in Jiashi county, Xinjiang (39.55°N, 77.15°E) with the focal depthof 25.2 km. The macroseismic epicenter located at the boundary of Bachu and Jiashi counties,Xinjiang Uygur Autonomous Region. 248 persons died and 4 853 ones were injured (2 058 ofthem were heavily injured) in the earthquake. 49 656 households (about 205 079 persons) losttheir houses. The Dis…     

Strong earthquake activity all over the world and strong—moderate earthquake activity within and near China（August,2002～September,2002）

Illustration All the data in this catalog are chosen from the (Preliminary Seismological Report of Chinese Seismic Stations( “Its abbreviation is "Monthly Report"). The catalog includes the events of M≥4.7 in and near China and M≥6 all over the world. The "Monthly Report" is monthly compiled by the Ninth Section of Institute of Geophysics, CSB.     

Is the invasion of the common reed,Phragmites australis,into tidal marshes of the eastern US an ecological disaster?

Studies of effects of the invasive brackish marsh plant Phragmites australis (common reed) on estuarine biota are reviewed. With few exceptions, most field studies indicate that these P. australis-dominated marshes have diverse and abundant benthic biota, and are utilized by nekton, comparable to Spartina alterniflora marshes. However, larval mummichogs, Fundulus heteroclitus, appear to be reduced in P. australis marshes compared with S. alterniflora marshes. Small epifauna living on plant stems also appear to be denser on S. alterniflora than P. australis stems. Other studies indicate that the detritus produced by decaying P. australis litter provides food value comparable to that of S. alterniflora and that its production enters estuarine food webs. Therefore, the general assumption that these marshes are ecologically "useless" is untrue. This information should be considered by marsh managers when making decisions about restoration projects.     

Strong motion characteristics of the M_w 6.6 Lushan earthquake,Sichuan,China——an insight into the spatial difference of a typical thrust fault earthquake

Near-field strong ground motions are useful for engineering seismology studies and seismic design, but dense observation networks of damaging earthquakes are still rare. In this study, based on the strong-motion data from the M w 6.6 Lushan earthquake, the ground motion parameters in different spatial regions are systematically analyzed, and the contributions from different effects, like the hanging-wall effect, directivity effect, and attenuation effect are separated to the extent possible. Different engineering parameters from the observed ground motions are compared with the local design response spectra and a new attenuation relation of Western China. General results indicate that the high frequency ground motion, like the peak ground acceleration, on two sides of the fault plane is sensitive to the hanging-wall effect, whereas the low frequency ground motion, like the long period spectral acceleration, in the rupture propagation direction is affected by the directivity effect. Moreover, although the M w 6.6 Lushan earthquake is not a large magnitude event, the spatial difference of ground motion is still obvious; thus, for a thrust faulting earthquake, in addition to the hanging effect, the directivity effect should also be considered.