In the past 2 years, three earthquakes of magnitude 6.0 and above occurred consecutively in Qinghai province, China, i.e., the 22 May 2021 M s 7.4 Maduo, 8 January 2022 M s 6.9 Menyuan, and 26 March 2022 M s 6.0 Delingha earthquakes. The hydrological observation instruments set up by the China Earthquake Administration allow us to study the dynamic processes in the well-aquifer systems during the establishment of criticality. Particularly, the observations played an important role in the prediction of the 8 January 2022 M s 6.9 Menyuan earthquake that was approved by the People’s Government of Qinghai province. This work presents the hydrological data recorded by 7 stations to show the short-term anomalies before these earthquakes. To explore the performance of the hydrological observations in detecting earthquakes that occurred on different active tectonic blocks, we calculate the relative amplitudes of the pre-seismic changes. Results indicate that markedly pre-seismic change is found if the observation station and the detection earthquake are on the same block, and moderate change is found if they are on the adjacent blocks, while the precursor is hard to be identified if they are on the separated blocks. The variations in the hydrological responses may be caused by the strength weakening (or dilatancy) of source media. And the increased volumes in the crust can be evidenced by the changes in the geodetic time series in the same neighborhoods and during the same period, augmenting stress loading between the blocks.

1 引言 为了能够有效记录学术交流实况,并有助于历次交流内容的查阅和检索,中国地震预报论坛2017—2019年期间的学术交流论文专辑在《国际地震动态》每年第8期出版.2020年度学术交流文集在《地震地磁观测与研究》2021年第2期以"中国地震预报论坛学术交流(2020)"专栏形式刊出,中国地震预报论坛2021年度学术交流文集在《地震地磁观测与研究》2021年增刊1刊出.中国地震预报论坛2022年度学术交流文集拟在本《地震地磁观测与研究》2022年增刊1刊出.自2022年开始,在Frontiers in Earth Science出版英文专辑,以扩大宣传中国在地震预报研究领域的最新进展.

利用决策树模型,基于五期土地利用评价因子,对甘肃省永靖县进行近40年的长时间尺度下的滑坡易发性评价,五期评价结果均显示研究区内滑坡灾害的极高和高易发性区域主要集中在中部黄河流域(盐锅峡镇至刘家峡水电站段)周边、西南部川城村—红泉镇—王台乡周边区域以及中部偏东的三条岘乡,该区域人口密集,人类活动较多.研究结果与前人研究结果类似,且通过受试者工作特征曲线的精度检验,说明五期评价结果均具有较高的可靠性.另外,研究区内的自然植被和裸土地与滑坡易发性指标之间具有负相关关系,而旱地、水域和城乡建设用地等人类活动频繁的区域则更容易导致滑坡灾害的发生.从时间尺度上来看,极高和高易发性分区面积逐年下降,但自2000年,极高和高易发性分区面积减少速度出现显著减缓,同期,该区域内的土地利用变化为城乡建设用地面积增加而植被面积减少,这使得区域内边坡稳定性下降,使部分防灾工程措施的减灾能力下降.本研究为该地区的灾害预防、预测和城乡土地规划提供了参考.

地震早期预警系统能够在震后数秒内快速估计地震影响,并通告可能受影响的区域,可以有效避免人员伤亡和财产损失.然而,传统地震早期预警系统需要耗费大量资金建设高密度地震台网.近些年,随着智能手机的普及,基于智能手机的地震早期预警(SEEW)研究受到广泛关注.SEEW系统的误警率和漏检率一直是研究的难点,也是影响系统实际应用部署的关键.采用深度学习、统计推断等模型构建了一种SEEW决策方法:①通过在长短时记忆(LSTM)模型中引入注意力机制,建立手机地震信号触发模型;②提出了一种基于时空一致的手机触发比例算子,并建立了基于统计推断的地震判别模型.通过仿真平台测试了方法性能,结果表明,该方法与类似方法相比,在极低的误警率下,地震成功预警率有显著提升.

Rupturing of the primary fault may trigger secondary fault activity in a complex multi-fault system. The mainshock focal mechanism and well-constrained aftershock locations reveal vital information about aftershock migration patterns, the regional tectonic stress field, and the seismogenic process. Aftershock relocations of the events in the Utah Mw5.7 earthquake sequence that occurred on March 18, 2020, indicate that the mainshock ruptured a listric normal fault; this fault is characterized by a shallow concave upward fault surface and a dip that decreases with depth. The aftershocks were largely organized into two clusters. The first small cluster, which is located ~ 8 km east of the mainshock, resides on part of a fault that is steeply dipping to the east; the second larger cluster is spread across multiple conjugate faults. Using local and regional waveforms to estimate the seismic moment tensor solutions, we determined that the Utah MW5.7 mainshock was a shallow crustal normal faulting event. Furthermore, 11 selected aftershocks (MW ≥ 3.3) are also characterized by normal faulting. The nearly EW-oriented extensional stress pattern in the focal area has an orientation that is similar to that of the regional maximum horizontal extensional stress field. Our analysis of the Coulomb stress variations showed that the Utah Mw5.7 earthquake triggered the aftershocks that formed along conjugate normal faults near the West Valley fault zone. These results provide evidence for the triggering hypothesis, wherein subsequent seismic events are caused by static stress changes triggered by large mainshock earthquakes.

The earthquake tendency consultations in China, which have been carried out by the China Earthquake Administration for more than 40 yr, are really forward prediction of earthquakes. The results, experiences, and data accumulation are valuable for seismic researches. In this article, the annual, monthly, and weekly predictions produced by the regular earthquake tendency consultations and the rapid postearthquake tendency prediction derived from the irregular ones are presented systematically. In the regular predictions, the areas where earthquakes tend to occur are identified by specific space-time windows. To evaluate the efficiency of the predictions, we apply the R-score method to all the medium-to-short-term efforts. The R-score has been used as a routine tool to test annual predictions in China, in which the hit rate and the percentage of spatial alarms over the whole territory are taken into consideration. Results show that the annual R-scores, during the period of 1990-2020, increased gradually, with the average of 0.293. The examples in 2018 indicate that a considerable proportion of earthquakes with the M-s 5.0 and above were detected by the annual prediction; some earthquakes were detected by the monthly prediction, whereas just only a few earthquakes could be detected by the weekly prediction. The corresponding R-scores are 0.46, 0.11, and 0.002, decreasing obviously with reduction of the prediction time windows, and the smallest one, which is very close to zero, may suggest the minimum time scale for an effective earthquake prediction. We also evaluated efficiency of the irregular predictions by analyzing the practices of 29 M-s >= 5.0 earthquakes since January 2019 and found that it is highly possible to do rapid postearthquake tendency prediction in China.

The analysis of post-seismic fault healing process is important for deepening our understanding of seismogenic mechanisms, seismic faulting theory, and seismic cycles. In this study, by using time series of continuous GPS stations from 2010.30 to 2013.30 between the Wenchuan earthquake and the Lushan earthquake, the dynamic evolution of fault locking and slip deficit rate in the middle-southern segment of the Longmenshan fault zone were inverted and analyzed by the negative dislocation program of TDEFNODE, and the healing process of the middle segment and the background of major earthquakes of the southwest segment were discussed based on the inversion results. The results show that the locking fraction of the ruptured area around the epicenter of the Wenchuan earthquake gradually increased, which was basically in creeping state in 2010, and then in state of strongly locked in 2013. The locked area also gradually increased from the southwest of the Wenchuan earthquake epicenter to the epicenter, which indicates that this part of the fault has been healing rapidly. Most of the ruptured zone in the northeast of the epicenter is still in creeping state and the fault has not yet begun healing. The fault near and southwest of the epicenter of the Lushan earthquake has been in state of strongly locked, and the slip deficit rate of the completely locked area has been decreasing year by year, probably indicating that the healed region shares part of the compression effect of the Bayan Har block on the Sichuan Basin. The above results indicate that the healing process and activity characteristics of different segments of the Longmenshan ruptured fault are significantly different after earthquake. The southwest segment of the Longmenshan fault zone is in state of strongly locked and the background for a major earthquake has strengthened in the case of rapid accumulation of compressive elastic strain.

建设中国地震预警系统是国家地震烈度速报与预警工程的主要内容,国内外学者通过对预警系统中确定地震参数的方法研究,发现实时确定准确震级这一问题最具挑战性,亟需一种可用的震级实时测定方法用于建设中国的地震预警系统.本文简要介绍了虚拟地震学家(VS)方法,描述了VS方法在中国地震台网用于实时测定地震参数的软件的实现流程,剖析用该方法实时确定2019年6月17日四川长宁6.0级地震的MVS的过程.通过实时在线测定134个M≥3.0地震的MVS和回放事件波形测定24个M≥5.0地震的MVS,对VS方法进行测试,评估其可用性.结果 表明,使用VS方法实时确定的MVS变化平稳,可用性较好.当3个台站的P波信息可用时,第一次测定MVS时偏差δ的平均值为0.32,δ≤0.5的占79％,平均用时为20s.随着时间的推移,更多可用台站及波形的使用可有效提升测定MVS准确度.该方法在中国地震台网的应用具有适用性和可行性,是一种可选的实时确定震级的方法,在地震预警中具有较好的应用潜力.

前震是短临地震预报最有效的方法之一.文中系统研究了1976—2017年全球29次MW≥8.0浅源地震的前震特征,发现:1)共有8次大地震出现前震,占总数的27.6％,且最大前震的震级M>5.0.这8次大地震均为逆冲型,占逆冲型地震总数(23次)的34.8％;2)前震序列的空间分布集中,且集中在主震震中周围.最大前震与主震的震中距为10～53km,震级差为1.1～2.8级.87.5％的时间差(最大前震与主震的发生时间差)为2h～15d,仅2006年11月15日千岛群岛8.3级地震前45d发生6.6级最大前震;3)与背景地震活动相比,前震具有高频次活动的特点.在8次大地震中,5次在主震前15d内加速活动;3次加速活动的开始时间超过1个月(35～45d),但在主震前1 d和6d又再次出现前震频次显著增多的现象;4)前震的震源机制解与主震一致,而余震的震源机制解比较复杂;5)使用ETAS模型计算前震和余震序列的参数 α、p和b值.为了确保参数计算的可靠性,文中约定当前震序列满足计算样本量N≥30且最低计算震级Mj≥Mc(Mc为最小完备震级)时,才同时计算前震和余震序列参数.此外,文中约定余震序列的持续时间为主震后1个月.在8次大地震中,有4个可以进行对比计算.结果显示,对于反映激发次级余震能力的 α值和序列衰减快慢的p值,前震和余震没有规律性差异;而反映应力水平的b值则共性特征明显,前震b值明显低于余震;与区域背景b值相比,前震b值低于区域背景b值的10％～24％.前震b值与区域背景b值之差是区域背景b值标准差的2.2～7.1倍,具有显著性.而余震b值高于区域背景b值或与其相当.为了讨论前震b值的稳定性,计算了2个资料丰富的前震序列的b值随样本量的变化.结果显示,在前震序列的开始阶段b值较低,之后逐渐增大,当计算样本量N≥70后,b值基本稳定.

文中利用干涉成像定位方法对2019年6月17日四川长宁MS6.0主震及部分余震进行定位.天然地震波振幅的极性和大小随震源机制和辐射花样的变化而变化,利用原始波形的特征函数可消除震源在不同方位上远场P波的初动极性和大小的不一致性.文中将干涉成像技术应用于天然地震定位,通过对干涉波形进行偏移和叠加处理,分别对震源的水平位置和深度进行偏移成像,确定了主震及较大余震(MS≥4.0)的震源位置参数,其中主震的位置为(28.38°N,104.88°E),震源深度为8.0km.此外,还测试了4种不同的速度模型对定位的影响,结果显示利用震源干涉成像定位方法获得的结果较为稳定.通过计算台阵、台网的响应函数,评估了台站分布及特征函数周期长短对定位结果的影响.计算得到的特征函数优势周期约为4s,该周期的台阵、台网响应函数在水平和垂直方向均显示了较好的收敛性和稳定性.

本研究以围绕着白龙江流域的甘肃省南部的宕昌县、舟曲县和武都区部分地区为研究区,根据全国滑坡编目中得到的272个历史滑坡数据以及选取的高程、坡度、坡向、平面曲率、剖面曲率、归一化植被指数(NDVI)、降雨、岩性、距道路距离和距河流距离10种影响因子,利用三种具有代表性的定量方法:信息量模型、以及基于频率比模型的逻辑回归模型和人工神经网络模型对研究区内滑坡灾害危险性进行评价.三种评价结果均显示研究区内滑坡灾害的极高和高危险区主要沿白龙江河谷地区呈带状分布.从危险性分区图可看出,人工神经网络模型得到的分区图较为合理,既表现出沿河谷地区集中分布的趋势,也呈现出对滑坡历史数据较为独立的特征,这一研究结果与前人研究结果一致.根据受试者工作特征曲线(ROC曲线)对三种模型的精度进行检验,检验得到的AUC值分别为0.818、0.829和0.837,说明三种评价结果均具有较高的可靠性,基于频率比模型的人工神经网络模型相比其他两个模型具有更好的评价精度,能更好地进行滑坡危险性的预测和评价,其中高程、降雨、岩性以及距道路距离对评价结果影响更大,这四种影响因子重要性值占比为52.1％.为该地区的城市扩建与灾害预防预测提供了参考.

The New National Standard (NNS) of earthquake magnitude have been used in the determination of earthquake magnitude. To estimate the magnitude impact of the NNS on the moderate-strong shallow earthquakes in quick report, the differences between the magnitudes of broad band surface wave (MS (BB)) and the magnitudes of old rapid determination are systematically analyzed based on the rapid report catalogue of M≥5.0 earthquakes in China mainland from 2001 to 2017. In addition, we make a comparative analysis on the MS (BB), MS (NEIC), MW (CENC) and MW (GCMT). The results show that the NNS magnitudes are basically consistent with that of the NEIC for M≥6. The frequencies of earthquakes with M≥5 and M≥6 decrease to about 60％ and 80％ of the original data, but difference is little when M≥6.5. The moment magnitudes estimated by China mainland are consistent with the international results. Because the earthquake magnitude is released using the moment magnitude in world and there is systematical difference between the moment magnitude and surface wave magnitude. Thus, we should take the moment magnitude as the rapid determination result in China to consistent with the international results. It may further decrease the frequency of M6 and M7 earthquakes.

为研究2008年汶川地震和2013年芦山地震前地壳形变特征,本文利用1999—2015年四期GPS速度场和1990—2017年跨断层短水准资料,对跨断层GPS速度剖面、GPS应变率场、断层闭锁程度和滑动亏损、跨断层年均垂直变化速率等进行了分析讨论,总结了汶川和芦山地震前后龙门山断裂带三维地壳变形演化特征.结果表明,汶川地震前龙门山断裂带中、北段处于强闭锁状态、断层面应力应变积累水平很高,而龙门山断裂带西南段闭锁较弱、变形速率明显高于中北段、依然可以积累应力应变,汶川地震震源位于闭锁相对弱的部位,这可能是导致汶川地震自初始破裂点沿龙门山断裂带向北东方向单侧破裂,而震中西南方向断层并没有发生破裂的原因之一.汶川地震的发生引起龙门山断裂带西南段应力应变积累速率加快、断层闭锁程度增强、闭锁面积增大,这在一定程度上促进了芦山地震的发生,而芦山地震震源位于汶川地震前强闭锁和弱闭锁的高梯度过渡部位.因为芦山地震只释放了龙门山断裂带西南段有限的应变能,并没有显著缓解该段的地震危险性,所以汶川和芦山地震之间的地震空段以及芦山地震西南方向的地震空段,依然需要持续关注.此外,本文还收集和对比分析了多次6～9级地震前地壳变形特征,同样显示地震成核于闭锁高梯度带区域而非完全闭锁区域内部,并且随着震级升高闭锁断层面的长度也在增大,这一现象还需在高分辨率形变数据的帮助下进行深入研究和分析.

Focal mechanism solutions and accurate source depths of earthquakes are important for understanding seismicity and structure of seismic faults. This work collected the seismic wave data of earthquakes with magnitudes M >= 5. 0 and 5. 0>M >= 4. 0,which occurred from January 1, 2010 to December 31, 2017, recorded by the national seismic network and the regional seismic network in Sichuan province. The focal mechanisms of these events were inverted applying the synthetic seismograms method. The results show that the earthquakes on the Longmenshan fault zone are of thrust focal mechanism. On the Xianshuihe fault zone, focal mechanism solutions are dominated by strike-slip. And in the southwest of the Sichuan-Yunnan block, normal faulting dominates the focal mechanism solutions. As the excitation energy of surface waves is sensitive to source depth, the surface wave amplitude spectrum is applied to determine the focal depth and compared with the results from China Earthquake Networks Center (CENC) , the U. S. Geological Survey (USGS), and the International Seismological Centre (ISC). The sources of the moderate-major earthquakes in the Sichuan region are mainly distributed in the upper-middle crust above 20 km. In the Longmenshan region, seismic sources are concentrated in the depth range from 10 km to 20 km. On the Xianshuihe fault zone, focal depths are confined about 10 km. In the southwest of Sichuan-Yunnan block, near the Litang and Jinshajiang faults, the depths of seismic sources are generally 5 km to 10 km.

本文应用ISOLA近震全波形方法,以2017年1月4日西藏仲巴4.7级地震为例,反演稀疏台网记录的中小地震震源机制解.该地震反演所得最佳双偶机制参数为:节面Ⅰ的走向109°/倾角85°/滑动角-177°,节面Ⅱ的走向19°/倾角88°/滑动角-4°,最佳矩心位置为30.590°N、83.784°E,最佳质心深度为6km,矩震级Mw4.6.震源机制反演结果表明此次地震是一次走滑型为主的事件,其与震源区域附近历史地震震源机制解具有相同性质.本文还应用CSPS初动扫描法,利用P波初动资料和近震波形联合约束反演此次地震的震源机制,并与ISOLA近震全波形反演结果进行比较,结果表明,联合少量台站的的三分量波形数据,能够定量地判断最佳震源机制解,降低了P波初动反演结果的非唯一性,同时也约束了由于少量台站参与全波形反演引起的解的不稳定性.本文研究为中小地震震源参数测定提供了一种简单有效的方法,具有较高的稳定性和可靠性.

We present a Pn wave velocity and anisotropy model of the central segment of the North-South Seismic Belt in China, where there are numerous stable basins and active faults, making this segment attractive for extensive studies. The model was obtained by a tomographic analysis of 49,973 Pn wave phase readings collected by the China Earthquake Networks Center and temporary stations in Yunnan and Sichuan. The tomographic velocity model shows that the average Pn wave velocity is 8.06 km/s; prominent high-velocity (high-V) anomalies are visible under the Sichuan Basin, the Zoige Basin and the Ordos block, which clearly outline their tectonic margins. A pronounced low-velocity (low-V) zone is observed from the Songpan-Ganzi block to the Chuan-Dian and Daliangshan blocks, suggesting the presence of hot material upwelling. The station delay data show a gradual variation from negative to positive values, possibly reflecting a crustal thickness variation from the southwest to the northeast of the study area. A correlation between the Pn wave anisotropy and the distribution of velocity anomalies is observed: anisotropy is relatively weaker in the high-V anomaly zones beneath stable basins, while it is stronger in the low-V anomaly zones and the high-to-low-V anomaly transition zones. The high-resolution velocity and anisotropy tomographic model that we obtained could also provide a better understanding of the study area seismicity, since the occurrence of strong earthquakes seems to be related to the presence and strength of lateral heterogeneities at the uppermost mantle level.

2008年5月12日汶川8.0级地震后,中国地震局组织专家经过系统的总结,认为300 km范围内震前只看到3％的前兆出现异常,震后再挖掘也只有6％的异常是客观事实,这可能是汶川地震没有预报,也没有办法预报的原因.但汶川地震后有部分学者提出了较多的前兆观测异常,说明300 km外前兆观测曾经看到异常现象.

在所有地震短临前兆中,前震是学术界公认的预报强震最有效的指标之一.由于有仪器记录的时间短,因此,有完整小震记录以来8级地震震例非常少.人们对地震序列的研究主要集中在5级以上地震.近年来全球发生了多次8级以上地震,为开展巨大地震序列研究提供了可能.本文系统研究了1973年以来全球MW≥8.0浅源地震的前震序列.研究中使用了美国国家地震信息中心发布的全球地震目录( http://earthquake.usgs.gov).地震目录的完备性分析结果显示,1973—1994年,该目录的最小完备震级位于4.6—5.0级之间变化;1995—2012年,最小完备性震级位于4.3—4.7级之间变化;2013—2016年,最小完备性震级位于4.2—4.6级之间变化.

In order to study the spatio-temporal evolution of the precursory anomalies 10 years before the 2008 Wenchuan Ms8.0 earthquake,the epicentral distance of the precursory anomalies is calculated by using the geometric center of the rupture region and the elliptical centerline of the aftershock region.The result shows that precursor anomalies gradually increase about 2 years before the Wenchuan earthquake.The ratio of abnormal items is greater than 25％ in the near the source area (about 2 times the source scale).The ratio of abnormal items is 17～24％ (about 3～5 times the source scale) in the remote area.There are three different stages of spatio-temporal evolution of precursory anomalies:during the α stage (including α1 and α2,700 to 3000 days before the main earthquake) the anomalies are mainly distributed in the southwest and the northwest area of the Wenchuan aftershocks area.It is shown that the precursors of the far source region and the near source area have the characteristics of outward expansion.During the 3 stage (300 to 700 days before the main earthquake),the anomalies are distributed in the southwest and northern regions of the aftershock region,showing a large range of anomalies.During the γ stage (Including γ1 and γ2,300 days before the main earthquake),the range of anomaly distribution is wide,and the anomalies are distributed in the Southwest and Northeast of the aftershock area.The anomalies contract to the epicenter (γ1) in the far source region and extend outward (γ2) in the near source region.Through the experimental study and mechanical analysis of earthquake preparation process,the results indicate that the threestage characteristics of precursory anomalies in the process of earthquake preparation may be controlled by the seismogenic body,which is a form of expression in the process of earthquake preparation and a universal feature during the earthquake preparation process.

On January 21,2016,a M6.4 earthquake occurred in Menyuan county,Qinghai Province.Its epicenter is located in the Qilian-Hexi Zoulang tectonic zone,which records several moderate-large historical earthquakes.Previous studies on this event are based on geology,remote sensing data and focal mechanism solutions,lacking analysis on its seismogenic structure.In order to study seismogenic fault plane and seismoteconic style of the earthquake,this work uses data of seismic intensity, aftershocks,and geology to address this issue.Furthermore,we calculate Coulomb stress changes imposed by the 1927 Gulang M8 and 1986 Menyuan M6.4 earthquake on the fault plane of the 2016 Menyuan M6.4 earthquake.The results indicate the early two events have posed distinct impacts on two nodal planes:loading or triggering on nodal plane Ⅰ,and unloading or delay on Ⅱ.In some cases such triggering stress is approaching or up to the threshold value of 0.01MPa.Combining isoseismals,aftershock distribution,geological structure and different Coulomb stress changes aforementioned,the nodal plane Ⅱ of the source model is considered the seismogenic feature.In conjunction with geophysical data,we establish the seismogenic model of the Menyuan earthquake, which is a positive flower structure in a profile,gentle in the upper and steep in the lower, characterized by thrusting in a strike slipping fault system.This is a possible model for thrusting earthquakes generated by strike-slip faults in a compressional tectonic regime.