Comprehensive precursor anomaly research based on earthquake corresponding relevancy spectrum

With the aim to the quantification of anomaly identification and extraction for observed or analyzed records, we present two statistical methods of earthquake corresponding relevancy spectrum （ECRS） and sliding mean relevancy （SMR）. With ECRS method, we can obtain the abnormal confidence attribute of data in different value ranges. Based on the relevancy spectrum in different studied time-intervals, we convert the original time sequence into relevancy time sequence, and can obtain the SMR time series by using the multi-point cumulative sliding mean method. Then we can identify the seismic precursor anomaly. We test this method by taking the time sequence of r/-value in the northern Tianshan region as original data. The result shows that when the studied time-interval is 18 months, the precursor anomaly can be identified bet- ter from sliding mean relevancy. The anomaly corresponding rate is 83 percent, the earthquake corresponding rate is 86 per- cent, and the anomaly is characteristic of the middle term. To try the research on multi-parameter comprehensive application, we take the Kalpin tectonic block in Xinjiang as our studied region, and analyze the spatial and temporal abnormal characters of multi-parameter sliding extreme-value relevancy （MSER） before mid-strong earthquakes in the Kalpin block. The result indicates that ECRS and SMR sequence in different time-intervals can not only be used to identify the precursor anomaly of single-item data, but also offer the data of quantitative single-item anomaly for comprehensive earthquake analysis and prediction.

Earthquake Electromagnetic Precursor Anomalies Detected by a New Ground-based Observation Network

It is a debated topic if there are any observable precursor anomalies prior to the earthquake(EQ hereafter)and if the stronger EQ can be successfully predicted.During last few decades quite a lot of observable electromagnetic(EM)precursors were published by using techniques equipped in either satellites or on ground-based stations.But there are only a few cases that the shortterm precursor anomalies of EM field before earthquakes were observed by using alternate EM fields on ground.This paper will present a new EM observation network built in recent years and show a new finding of EM field with the variation of a one-year cycle observed using the network.As an example,the short-term precursor anomalies of apparent resistivity before the Yangbi EQ(Ms 5.1)occurred on March 27,2017 in Yunnan Province will be studied.The observed anomalous phenomena indicate that the anomaly before the EQ can be captured only if reasonable effective methods including sophisticated analytical techniques are used,and it is believed that continuously observed data on the fixed observation network for a long time is an effective means for studying anomalies that appeared before earthquakes.This network can also play an important role in studying the EM environment from space.

ANALYSIS ON SHORT-TERM PRECURSORY ANOMALIES AND SEQUENCE CHARACTERISTIC OF NINGLANG EARTHQUAKE 1998

From Octobet 1998 to January 1999,5 earthquakes ( M s≥5) occurred between Ninglang and Yanyuan counties (27°07′～27°12′N,100°40′～101°00′E area).They were situated in 140km southwest of the Xichang.Among them,the largest one is M s 6 2 on November 19,1998.Based on small seismic data by the seismic remote sensing station of Xichang and the seismological station of Muli,and regional observation data,passing through careful observation and scientific analyses,we had made better forecasts before the earthquakes.That results obvious social benefits.By processing data of precursory earthquakes,such as,original observation data of total geomagnetic intensity from the station of Xichang,pressure capacitance stressometer and quartz horizaontal pendulum tiltmeter from the Xiaomiao station of Xichang,we summarized the sequence characteristics of the series earthquakes.The information about short\|term anomaly of gruond strain,total geomagnetic intensity and ground tilt before the earthquake is emphatically explained.

Temporal and Spatial Evolution of Precursory Anomalies of the Wenchuan MS8.0 Earthquake and Their Mechanical Analysis

In order to study the spatiotemporal evolution of the precursory anomalies 10 years before the Wenchuan M_S8. 0 earthquake in 2008, 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, precursor anomalies gradually increased about 2 years before the Wenchuan earthquake. The ratio of abnormal items is greater than 25% in the near source area (about twice the source scale) and 17%-24% in the remote area (about 3-5 times the source scale). There are three different stages of spatiotemporal evolution of precursory anomalies. During the α stage (including α_1 and α_2,between 700 to 3000 days before the main earthquake),the anomalies are mainly distributed in the southwest and 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 β stage (between 300 to 700 days before the main earthquake), the anomalies are distributed in the southwest and northern region of the aftershock region, showing a large range of anomalies. During the γ stage (including γ_1 and γ_2, 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 converged to epicenter (γ_1) in the far source region and expand outwards (γ_2) in the near source region. Results of the experimental study and mechanical analysis of earthquake preparation process indicate that the three-stage 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 featureduring the earthquake preparation process,which has a certain guiding role in earthquake prediction.

The Characteristics of the Precursory Anomaly prior to the Yiliang Earthquakes,Yunnan,China on September 7,2012

An analysis was carried out on the seismic activity and the precursory anomaly prior to the earthquakes in Yiliang on September 7,2012. The characteristics of the seismic activity,the dynamic changes of underground fluid and deformation were investigated. As a result of the investigation,we found that: before the earthquake,the seismicity level of M4. 0earthquakes had enhanced,and seismic gap of a small earthquake had appeared; the precursory anomalies emerged about 1 year before the earthquake; there was phenomenon of short-term anomaly migrating from the periphery to the epicenter area; the imminent anomaly appeared in a relatively concentrated period of time, a week before the earthquake. The research has shown a significant guidance for the analysis and prediction of strong earthquakes( Ml> 5. 0).

The Contrast Study of Precursor Anomalies before the M_S 8. 0 Wenchuan Earthquake

The contrast research results show that the number of items and stations with imminent, short and medium term precursor anomalies for the Wenchuan M_S 8. 0 earthquake is less than that of the Menglian earthquake. The number of anomalies and stations associated with the Wenchuan earthquake increased in the early stage of the short-term range,as opposed to the later period for the Menglian and Lijiang earthquakes. Most of the medium term anomalies occurred two to three years before the Wenchuan earthquake,when the number of anomaly stations and items was eleven,and a great change appeared in the observation values in about half of the stations ( items ) . However,for the Menglian earthquake,medium term anomalies happened one to two years before the earthquake, the number of abnormal stations and items reached 20,and a sharp change appeared in the observation values six months to one year before the earthquake in about 30 percent of the stations or items. In the epicenter and the nearby area,the macroscopic abnormalities started 3 years before the Wenchuan earthquake and lasted intermittently until 1 month before the earthquake. Within 2 percent of the total area of the province,the macroscopic abnormalities accounted for 30 to 50 percent of the total number of anomalies of the Province. For the Xingtai,Tangshan,Haicheng,Songpan earthquakes,the macroscopic anomalies started two to three months before,or on the very day of the earthquakes. The common feature of the precursors between the Wenchuan and other strong earthquakes is the appearance of tremendous changes in a certain number of observation values of anomalies in the mid and short terms before all these earthquakes.

基于GPR-LSTM的地震热红外背景场的构建方法

地震监测是一项非常重要且具有挑战性的任务,遥感技术的不断发展加强了在宏观尺度上对地球表面的监测能力。研究表明,地震前通常都会出现地表温度异常升高的现象,因此各种异常提取算法被应用于地震热异常研究中。其中,基于背景场的提取方法由于具有较强的机理解释性而受到广泛应用。然而,以往基于背景场的异常提取方法更多将背景场限定于某一固定阈值,忽略了受外界因素(非震)影响导致的地表温度的小范围正常波动。据此,文中提出了一种基于GPR-LSTM的地震热红外背景场的构建方法。该方法包括两大部分:震期年变基准场的建立、实际LST的残差波动范围计算及背景场的构建。基于MODIS地表温度产品,以2008年四川汶川和新疆于田地震为研究对象,使用所述方法对地震前兆热异常信息进行提取与分析,经过实验得出以下结论:1)地震热异常通常沿青藏高原的断层分布,这不仅证明了文中方法能够减弱地表温度数据中噪声的干扰,同时也证明该方法在热异常信息提取方面的有效性;2)地震年份的构造活动比非地震年份更加活跃,导致地表温度的异常增温更加明显;3)不同地震案例震前的热异常时空特征各不相同。

Variations of Atmospheric ELF/VLF Radio Noise Due to Seismogenic Modifications in Tropospheric Conductivity

We suggest a possible explanation of the influence of pre-seismic activity on the registration rate of natural ELF(extremely low frequency)/VLF(very low frequency) pulses and the changes of their characteristics. The main idea is as follows. The distribution of the electric field around a thundercloud depends on the conductivity profile of the atmosphere. Quasi-static electric fields of a thundercloud decrease in those tropospheric regions where an increase of air conductivity is generated by pre-seismic activities due to emanation of radioactive gas and water into the lower atmosphere. The electric field becomes reduced in the lower troposphere, and the probability decreases of the cloud-to-ground (CG) strokes in such “contaminated” areas. Simultaneously, the electric field grows inside and above the thunderclouds, and hence, we anticipate a growth in the number of horizontal and tilted inter-cloud (or intra-cloud) (both termed as IC discharges) strokes. Spatial orientation of lightning strokes reduces vertical projection of their individual amplitudes, while the rate (median number strokes per a unit time) of discharges grows. We demonstrate that channel tilt of strokes modifies the spectral content of ELF/VLF radio noise and changes the rate of detected pulses during the earthquake preparation phase.

藏东地区地震前兆宏观异常的站网建设与展望

在藏东地区,有丰富的温泉、众多河流和发达的养殖场,宏观异常现象频繁,因此成为研究地震前兆的重要地域。建设地震前兆宏观异常站网对该地区的地震研究非常重要,能提供实时数据支持和增强地震前兆现象的系统研究。通过站网的建设,可以收集大量准确的数据并进行系统分析和研究,为地震科学领域提供新的研究思路和方法。因此,在这一独特地域建设相应的站网至关重要。

Detection of ULF electromagnetic emissions as a precursor to two earthquakes in China

The geomagnetic data recorded by Kashi and Jinghai observatories in China were analyzed with improved polarization method. We compared the result around 0.01 Hz which is thought to be useful to detect the ULF anomaly with the result around 0.1 Hz which was inferred from the earthquake depth according to the skin effect, and found that 0.1 Hz is more proper to detect the ULF anomaly for both earthquakes studied in this paper.

Abnormal Phenomena Recorded by Several Earthquake Precursor Observation Instruments Before the M_s 8.0 Wenchuan,Sichuan Earthquake

The paper introduces the anomalies observed by digital tiltmeter, cross-fault deformation meter, 4-component borehole strainmeter and geothermometer before May 12, 2008, Ms8.0 Wenchuan earthquake, Sichuan. The digital tiltmeter installed in the epicentral region in Shifang County recorded the tilt anomalies 15 days before the earthquake with variation amplitude of 3.7 times larger than the annual deviation of 2007. The cross-fault deformation meter installed at Zimakua station on the Xianshuihe-Anninghe fault zone detected displacement anomaly occurring since 2006 with the variation amplitude exceeding the cumulative value of the last ten years. Five borehole strainmeter stations in the Chongqing section of Three Gorges Reservoir area observed unconventional strain changes occurring in the period from May 1 through 12, 2008. Among them, the strainmeter at Wanzhou station recorded the great compression strain rate on the EW component at 14：00 o＇clock of May 10, and the anomaly amplitude was so large that the instrument output exceeded its dynamic range, corresponding to a level of -10^4 nanostrains. The geothermometers installed in Xi＇an, Chongqing and Xichang recorded the sudden temperature changes from November 2007 to January 2008 with the variation amplitudes several times larger than the ordinary deviation. The above phenomena and the criteria for distinguishing the anomalies from background fluctuations are discussed in this paper.

Ionospheric VTEC anomalies before Ms7.1 Yushu earthquake

Vertical total electron content is examined to check whether the Ms7.1 Yushu earthquake on April 14, 2010, may have caused any anomalous ionospheric changes. The result shows two TEC increases over the epicenter vicinity on April 1 and 5; these anomalies drifted from east to west, the latter across the whole China. The increase on April 5 was probably related to geomagnetic activity, whereas the one on April 1 may pos- sibly be related to the Yushu earthquake.

Probable satellite thermal infrared anomaly before the Zhangbei M_s=6.2 earthquake on January 10, 1998

This paper used the thermal infrared data of the satellite NOAA-AAVHRR of the north pat of North China (113°~119°E, 38°~42°N), and processed the remote sensing data through radiation adjustment, geometric adjust ment and so on by the software 'The Monitoring and Fast Process System of Earthquake Precursor Thermal Infra red Anomaly', inversed the each surface temperature. Some disturbances effect had been excluded, and thermal infrared temperature anomaly had been extracted by the picture difference method. The Zhangbei M_s=6.2 earth quake is used as the example in the paper, so that in the paper thermal infrared characteristics on time-space before earthquake and the relationship between the anomaly and the earthquake prediction have been summarized. Within more than ten days before the Zhangbei earthquake, the thermal infrared anomaly had emerged widely along Zhangjiakou-Bobal seismic belt, and the anomalous region seemed like a belt and it is also consistent with the tectonic background there; the anomaly expanded from the outside toward the earthquake focus, but the focus lay at the edge of the thermal infrared region. So it is possible to explore a new anomaly observation method for earthquake prediction by observing and studying the satellite thermal infrared anomaly before big earthquakes happen.

Analysis on the Characteristics of the Kalpin Ms5.3 Earthquake Sequence of December 1,2013 and Anomalies before the Earthquake

This paper introduces the basic parameters,focal mechanism solutions and earthquake sequence characteristics of the Kalpin M_S5.3 earthquake sequence of December 1,2013,and analyzed seismic activity before the earthquake,the adjacent tectonic features and the precursory anomaly at fixed points within a range of 200 km. Research indicates:(1) The earthquake occurred on Kalpin fault,the source rupture type is thrust faulting with sinistral strike-slip component.( 2) The earthquake sequence is mainshock-aftershock type,with the aftershock distribution attenuating quickly and trending NE.(3) Abnormal seismic activity before the earthquake was characterized by seismically nesting quiescence of MS2. 0-4. 0 earthquakes,seismic quiescence of MS4. 0 earthquakes and seismic belts of MS3. 0 earthquakes in the Kalpin block, abnormal enhancement zone of moderate earthquakes on Puchang fault and seismological parameters.(4) Anomalies of precursory observation data at fixed stations are mainly characterized by mutation. Apart from the borehole tiltmeter in Halajun, the spatial distribution of other abnormal precursors showed a phenomenon of migration from the near field to far field and from the epicenter to the peripheries.

Simultaneous Study of VLF/ULF Anomalies Associated with Earthquakes in Japan

We carried out a simultaneous study of ground-based magnetic field and lower ionospheric anomalies during major earthquakes occurring around Japan in 2010 and 2012. Ultra Low Frequency (ULF) geomagnetic field waveforms of Esashi station and Very Low Frequency (VLF) Japanese transmitter (JJY) electric signal amplitude received in Moshiri station Hokkaido during nighttime (22:00-02:00 LT) were used to minimize the local interference. Twenty earthquakes having magnitude greater than 5.5 were considered for the data analysis for two years. Nighttime amplitude fluctuations and polarization from the received VLF transmitter signal amplitude and ULF magnetic field respectively were calculated to identify anomalous signatures in relation to every earthquake. We found most earthquakes analyzed indicating VLF amplitude anomalies simultaneously occurred with ULF magnetic field anomalies within a week prior to the earthquakes. Stronger anomalies were observed for larger magnitude and shallower earthquakes. Focal mechanism of earthquakes was also examined to identify the effectiveness of generating anomaly. Both VLF and ULF anomalies were observed for reverse fault type earthquakes occurring under the strong pressure in the crust. Obtained results may indicate the common anomaly source both for VLF and ULF in the lithosphere and are consistent with currently proposed Lithosphere-Atmosphere-Ionosphere (LAI) coupling scenarios during the earthquake preparation period.

Electromagnetic Precursors to the 2016 Kumamoto Earthquakes

The Kumamoto area of Kyusyu Island was attacked by a series of large earthquakes (EQs) in April, 2016. The first two foreshocks had the magnitudes of 6.5 and 6.4, and about 1 day later there was the main shock on 15 April (UT) with magnitude 7.3. These are fault-type EQs, and so we would expect a variety of electromagnetic precursors to these EQs because we had detected different phenomena for the 1995 Kobe EQ, same fault-type EQ. As for the lithospheric effect, the ULF data at Kanoya observatory (about 150 km from the EQ epicenters) are used, but the simple statistical analysis could not provide us with any clear evidence of ULF radiation from the lithosphere. However, our conventional analyses indicated clear signatures in the atmosphere as ULF/ELF impulsive emissions and also in the ionosphere as observed by means of VLF propagation anomalies and ULF depression. ULF/ELF radiation appeared on 8-11 April (in UT) (maximum on 10 and 11 April (UT)), while ULF depression took place on 8 and 10 April (in UT), so that both atmospheric radiation and ionospheric perturbation took place nearly during the same time period.

The Application of Wavelet Transform in Analysis of Digital Precursory Observational Data

Digital data of precursors is noted for its high accuracy. Therefore, it is important to extract the high frequency information from the low ones in the digital data of precursors and to discriminate between the trend anomalies and the short-term anomalies. This paper presents a method to separate the high frequency information from the low ones by using the wavelet transform to analyze the digital data of precursors, and illustrates with examples the train of thoughts of discriminating the short-term anomalies from trend anomalies by using the wavelet transform, thus provide a new effective approach for extracting the short-term and trend anomalies from the digital data of precursors.

2021年青海玛多M_(S)7.4地震前电磁异常时空演化特征

1研究背景。地震电磁分析预报方法在近年震情跟踪工作中的作用已日益突出,显示了良好的应用前景;与此同时,通过众多学者总结归纳的指标(中国地震局监测预报司,2020)已作为目前地震电磁异常重要的识别线索和地震预测参考依据。自2015年开始中国地震局电磁分析预报技术管理组组织人员开展了地震电磁分析预报方法指标研制与完善,共研制完善9个方法。

门源M_(S)6.9地震前后地震异常时空演化

中国大陆发生强震动力来源主要是在印度—欧亚板块碰撞下,青藏高原的北向运动、东部地区的东向运动作用(Wang and Shen,2020);近20年青藏高原北缘地块运动主流观点是巴颜喀拉块体向东运动带动周边地块的运动,但从近十年的地震活动分析,柴达木和祁连块体向东运动是增强的,2022年门源M_(S)6.9地震等一系列地震是典型的震例。

地震引起的超导重力异常数据分析

地震给人类造成重大的伤亡和经济损失,但目前尚未能够找到准确预测地震的有效途径。有学者发现在地震发生前超导重力仪可能会观测到重力异常,如某些地震爆发前,会出现种类似“喇叭状”的异常,这种异常是不是可信的地震前兆还值得进步研究。