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从异年倍九法(或称异年倍九律)讨论了华北7级以上大震发生日期之间的关系。这种关系对今后在类似季节预测大震的发生日期有一定的参考作用。 相似文献
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一个震群发生后,迅速判断该震群是“大震”的前震序列,还是并不伴有大震发生的一般震群,对减轻地震灾害和维护社会稳定具有重要的现实意义.本文通过辽宁省境内发生的部分震群类型做了系统地对比分析和研究,提出前震序列型震群的概念. 相似文献
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本文在1977年以来提出的“予报地震的倍九律”基础上,研究了我国很多地震区大震的异年倍九现象,进一步提出了“异年倍九律”。异年倍九律是指相近地区不同年份大震发震日序间具有倍九日关系的情况。由于大震日期予报至为重要,所以本文仅以7级和7级以上大震进行统计。统计发现我国许多地震区大地震发生日期符合上述异年倍九律现象。这些地区是渤海至燕山前麓地震区,山东郯城潍坊地震区,武都茂汶地震区,四川巴塘、理塘地震区,炉霍、道孚地震区,云南东川、嵩明地震区,西藏墨脱至米林地震带,当雄至奇林湖地震区,新疆巴里坤地震区,乌恰地震区和富蕴至中蒙边境阿尔泰地震带。由这十一个地区异年倍九的震例来看,地震日序差值以36天的频次最高,约占总的统计数40%,月份大多出现在6—9月。此外符合这种时间规律的地区不是杂乱的,例如汾渭地震带就不符合这种规律。因此异年倍九律对某些已有短期震兆的地震危险区发布大震的发震日期有一定参考作用。异年地震发震日期的倍九律具有较多的统计事实表明,这种现象的出现不是偶然的。作者认为相差几十年和几百年的大震,它们发震的月份相近,且发生地震的日期符合倍九律可能与这些地区在这段时期具有倍九时间特征的外因较强有关。也即与外因对地震的调制作用有关。具体的调制因素和调制机制尚需进一步研究。初步认为可能是气象因素、磁暴,日月引力等外因因素对地震的发生起到了调制作用,以上这三种外因均有倍九天的周期成份,如这三种倍九天的周期成份在某些地区某些时间产生合拍运动,则就可能增加外因对地震的作用。在自然界除了研究可公度性和周期性现象外,还要研究走向混沌的道路。我们发现,两大类事物分别走向混沌的临界常数A和B,与黄金分割数C之间有一简单关系,即: 2 A-B=C 式中A=4.66920,B=8.7210,C=0.618(此亦为优选法中的常数)。 相似文献
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带头地震是异年倍九律时间系列中的头一个地震,其震级较大。在它发生后几百年内附近200—300公里范围的6级和6级以上地震与它的发生日期往往呈倍九天的关系,其月份范围在带头地震发生日期前后2—3个月内。已发现的带头地震有1679年三河平谷大震,1668年郎城大震,1624年扬州大震,1604年泉州东大震。另外还发现在中国西部也有不少带头地震。带头地震和随后的被带地震其间的倍九律关系可能是具有倍九天可公度的外因调制地下过程的结果。在前兆观测的基础上用带头地震有助于选择发震日期。 相似文献
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前震和普通震群震源深度分布的比较 总被引:2,自引:4,他引:2
本文从强固区模型和地壳应力分布特点出发,讨论了前震和普通震群在震源深度分布上的差异性。分析中国大陆39组震群震源深度数据。结果表明,普通震群多数分布在强度较低的上地壳,前震和前兆震群比普通震群要深得多,可能达到中下地壳,差别显著。为减小测深误差的影响,建议把相对深度特征值△H作为一种识别前震和普通震群的可能标志。普通震群最大深度H_(max)一般≤16km,而前震的H_(max)均>16km。震群的震源垂直尺度△H_1≤10km,而前震的△H_1>10km。震群的最大深度距平值△H_2≤6km,而前震的△H_2>6km。 相似文献
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Introduction The characteristics of generalized foreshock and direct foreshock and their identification,as well as their application to medium and short-term prediction of strong earthquake is a major study objective in seismometry both in China and abroad.China has made many short-term and imminent earthquake predictions.Among the ones with clear hazard-mitigating effect and social manifestation,direct foreshock has made an obvious contribution,for example,the MS=7.2Menglian earthquake occu… 相似文献
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Using the match-and-locate method to characterize foreshocks of the July 2019 MW6.4 Ridgecrest,California earthquake 下载免费PDF全文
The July 2019 MW6.4 Ridgecrest, California earthquake and its distinct foreshocks were well recorded by local and regional stations, providing a great opportunity to characterize its foreshocks and investigate the nucleation mechanisms of the mainshock. In this study, we utilized the match-and-locate (M&L) method to build a high-precision foreshock catalog for this MW6.4 earthquake. Compared with the sequential location methods (matched-filter + cross-correlation-based hypoDD), our new catalog contains more events with higher location accuracy. The MW6.4 mainshock was preceded by 40 foreshocks within ~2 h (on July 4, 2019 from 15:35:29 to 17:32:52, UTC). Their spatiotemporal distribution revealed a complex seismogenic structure consisting of multiple fault strands, which were connected as a throughgoing fault by later foreshocks and eventually accommodated the 2019 MW6.4 mainshock. To better understand the nucleation mechanism, we determined the rupture dimension of the largest ML4.0 foreshock by calculating its initial rupture and centroid points using the M&L method. By estimating Coulomb stress change we suggested that the majority of foreshocks following the ML4.0 event and MW6.4 mainshock occurred within regions of increasing Coulomb stress, indicating that they were triggered by stress transfer. The nucleation process before the ML4.0 event remains unclear due to the insufficient sampling rate of waveforms and small magnitude of events. Thus, our study demonstrates that the M&L method has superior detection and location ability, showing potential for studies that require high-precision location (e.g., earthquake nucleation). 相似文献
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2018年9月4日新疆伽师发生MS5.5地震,震中处于塔里木地块西北缘,位于1997~1998年伽师强震群震区内。此次伽师地震前发生了MS4.7前震,截至9月30日最大余震震级为MS4.6(ML5.0),初步判定为前-主-余型地震序列。序列精定位结果显示,余震沿近NE向展布,主震震源深度与1997~1998年伽师强震主震基本一致,发震断层陡立。本文从区域的构造环境、地震震源机制解和余震分布特征等方面分析认为,地震发生在伽师隐伏断裂东南端部,为1997~1998年伽师强震群震区的一次新的构造活动。序列参数、视应力等计算结果显示,伽师MS5.5地震的预测最大余震震级与最大余震震级MS4.6接近,表明序列最大余震已经发生。 相似文献
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In this paper changes in focal mechanisms) parameters of wave spectra, and stress drops for the Ms=5.0 forcshock and Ms=6.0 mainshock in February 2001 in Yajiang County, Sichuan, and seismicity in cpiccntral region are studied. Comparison of focal mechanisms for the Yajiang earthquakes with distribution patterns of aftcrshocks, the nodal plane Ⅰ, striking in the direction of NEN, of the Yajiang M=5.0 event is chosen as the faulting plane, the nodal plane Ⅱ, striking in the direction of WNW, of the M=6.0 event as the faulting plane. The strikes of the two faulting planes are nearly perpendicular to each other. The level of stress drops in the cpicentral region before the occurrence of the M=6.0 earthquake increases, which is consistent with increase of seismicity in the epicentral region. The rate decay of the Yajiang earthquake sequence, changes in wave spectra for foreshocks and aftershocks,and focal mechanisms are complex. 相似文献
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On September 3rd (22:07 UTC), 1997 a small earthquake with Mw=4.54 started the foreshocks sequence (1500 events with ML <3.1) of the September 26th seismic sequence. Two days after, three seismic stations of the University of Camerino were installed around the macroseismic epicenter of the foreshock. We present in this paper the location of foreshocks (with 2.1L<3.3) which occurred between September 3rd and 26th. Foreshocks location, with horizontal (ERH) and vertical (ERZ) error less than 1.5 km, define an area 4 km large. Foreshocks have been localized between the epicenters of the two major events of September 26th, which occurred at 00:33 UTC with Mw=5.6 and at 09:40 UTC with Mw=6.0 (Amato et al., 1998; Ekström et al., 1998). In a vertical cross-section, hypocenters show a low angle (30°) structure with SW dip-direction. Focal mechanisms for three of the major events show dip-slip fault solutions with strike direction of about N130, in agreement with the CMT solutions of September 3rd and September 26th earthquakes (Ekström et al., 1998). Data recorded at two stations Popola (POP) e Capodacqua (CPQ) located on the rupture area of the September 26th faults, allowed us to calculate a mean Vp/Vs ratio of 1.84±0.03 for the foreshock. This value is lower than the Vp/Vs ratio of 1.89±0.02 calculated for the aftershock sequence occurred in the same area. Besides, the Vp/Vs ratio during the foreshocks sequence is not stable in time but it seems to increase approaching September 26th. After September 26th mainshocks, this value tends to stabilize around a higher value of 1.89. Following the dilatancy model, we suggest that the relative low Vp/Vs ratio before the main shocks could indicate the presence of fluid in the focal volume. The presence of fluids could have increased the effective stress on the fault plane and could be responsible for the long foreshock activity before the two main earthquakes of September 26th. Therefore, we suggest that this foreshock activity could have also contributed to reduce the friction along the September 26th fault plane, breaking the active structure in two smaller segments. In this hypothesis, foreshock activity could have drastically contributed to mitigate the seismic potential of the Colfiorito's active structure. 相似文献
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Based on the seismic phase reports of the Yangbi area from January 1 to June 25, 2021, and the waveform data of M ≥ 4 earthquakes, we obtained the relocation results and focal mechanism solutions of the MS6.4 Yangbi earthquake sequence using the HypoDD and CAP methods. Based on our results, our main conclusions are as follows: (1) the MS6.4 Yangbi earthquake sequence is a typical foreshock-mainshock-aftershock sequence. The foreshocks of the first two stages have the obvious fronts of migration and their migration rate increased gradually. There was no apparent front of migration during the third stage, and the occurrence of the mainshock was related to stress triggering from a M5.3 foreshock. We tentatively speculate that the rupture pattern of the Yangbi earthquake sequence conforms to the cascading-rupture model; and (2) the main fault of the MS6.4 Yangbi earthquake sequence is a NW-trending right-lateral strike-slip fault. As time progressed, a minor conjugate aftershock belt formed at the northwest end of this fault, and a dendritic branching structure emerged in the southern fault segment, showing a complex seismogenic fault structure. We suggested that the fault of the Yangbi earthquake sequence may be a young sub-fault of the Weixi-Weishan fault. 相似文献
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Yanyan Han Yang Zang Lingyuan Meng Yue Wang Shiguang Deng Yawei Ma Mengyu Xie 《地震研究进展(英文)》2022,2(3):100157
In this article, we review the general characteristics of seismicity in and around China and the overall statistics of earthquake damage in 2021, focusing on several significant events and related scientific topics. Among them, the largest event is the MS 7.4 Madoi earthquake in Qinghai Province, northwest China. The event marks another MS ?≥ ?7 earthquake occurring near the boundary of the Bayan Har Block that has ended a remarkable quiescence of the MS ?≥ ?7 earthquakes within the Chinese mainland. In addition, the MS 6.4 Yangbi earthquake in Yunnan Province, southwest China draws the most attention because of its abundant foreshocks, which are well recorded by the densely distributed seismic stations in the surrounding regions. Regarding this event, we review several recent publications focusing on the Gutenberg-Richter b-value change and the physical mechanism of foreshocks associated with this sequence. The MS 6.0 Luxian earthquake in Sichuan Province, southwest China has caused serious damage with a relatively low magnitude, partly because the focal depth of the mainshock is relatively shallow (3.5 ?km). It is another strong earthquake occurring within the southeast Sichuan basin with low historical seismicity yet has increased significantly since 2015, probably due to shale gas development and associated hydraulic fracturing. 相似文献