前兆性地震平静研究

作为一种重要的强震前兆现象, 地震平静有可能提供关于地震位置、时间和大小的有用信息,在地震预测中将具有重要作用.为全面了解地震平静这一极具希望的前兆现象,本文将详细地阐述地震平静的定义、研究方法、存在规律、模型及其可能的物理机制,并对存在的问题与未来的发展提出初步的设想.     

Case 23 nomination of precursory seismic quiescence as a significant precursor

Conclusions Several cases of extremely strong quiescences have been investigated in great detail, and it was found that they are statistically highly significant and that they cannot be reasonably explained by catalog heterogeneity. Several additional cases of quantitatively measured quiescence have been documented. The method of measuring quiescence has progressed from using visual means to using a quantitative approach, and the understanding of the noise sources has significantly advanced during the last few years. Therefore I feel that quiescence is a real phenomenon and the method to detect it has matured to a point that is acceptable for the List of Significant Precursors, although considerably more work needs to be done to understand this parameter and its role in the earthquake generation process.     

Evaluation of precursory seismic quiescence in sixteen subduction zones using single-link cluster analysis

This paper describes a new method, single-link cluster analysis (SLC), to evaluate percursory quiescence for shallow earthquakes in sixteen subduction zones, using data from the ISC catalog. To define quiescent regions, we divided the catalog into time intervals with a durationT, overlapping byT/2. We considered all earthquakes having magnitudes larger than some magnitudeM _min, lying within a specified distance of a great circle which is approximately coincident with the trench near a subduction zone. Within each time interval we connected or linked all earthquakes lying within some cutoff distanced of one another. We then projected all these links onto the great circle, and defined a region to be quiescent if it was not covered by the projection of any links. For this study,T was two years,M _min wasm _b =4.9, and we variedd from 100 to 400 km. We defined an earthquake as following quiescence if it occurred within two years following, and within 75 km of a quiescent zone as defined above. The primary conclusion of this study was that earthquakes with surface wave magnitudes 7.2 and greater were about 5–15% more likely to follow quiescence than were the smaller background earthquakes withm _b >-4.9. A chi-squared analysis shows that this result is significant at the 99% level. In contrast, earthquakes with surface wave magnitude of 6.7 to 7.1 were no more likely to follow quiescence than were background earthquakes. Of sixteen individual regions, Central America, Japan, and Peru-Chile were the only regions where large earthquakes were more likely to occur following quiescence than were background earthquakes. For a cutoff link length of 300 km, only in Central America was the difference between large earthquakes and background earthquakes significant at the 95% level of significance. For a cutoff link length of 250 km, the significance level exceeded 95% only in Japan. The SLC method is an objective, quantitative method for evaluating large data catalogs, or for monitoring quiescence in regions where quiescence is conjectured to precede large earthquakes.     

喀什-乌恰地区近年来强震活动平静的可能成因

通过分析喀什—乌恰地区和伽师—柯坪块区强震产生的静态库仑破裂应力变化(ΔCFS), 从断层相互作用和中等地震活动加、 减速特征的角度, 初步论证了两个区域强震活动交替发生特征的可能机理。 库仑破裂应力和加速矩释放模型拟合结果表明, 伽师—柯坪地区1997—1998年成组发生的伽师6级强震、 新疆南部周边发生的1992年苏萨梅尔M_S7.5地震和2005年巴基斯坦7.8级地震产生的静态应力变化不利于喀什—乌恰地区强震的发生, 可能使得该区后续强震的发生时间延迟了。 另一方面, 位于1992年苏萨梅尔M_S7.5地震和1997—2003年伽师系列强震产生的ΔCFS为负的喀什—乌恰地区地震活动表现为弱加速特征, 这或许是1993年以来喀什—乌恰地区强震平静特征的原因。 喀什—乌恰地区7级地震产生的正的ΔCFS可能有利于伽师—柯坪地区后续强震的发生, 3组7级地震产生的ΔCFS为正的区域内后续强震发生前均出现了一定程度的加速特征, 从而定量解释了喀什—乌恰地区强震活动对伽师—柯坪块区地震活动的影响。     

Palaeoseismic history of the eastern part of the North Anatolian Fault (Erzincan,Turkey): Implications for the seismicity of the Yedisu seismic gap

The North Anatolian Fault showed a remarkable seismic activity especially between 1939 and 1999, when the westward migrating earthquake sequence created surface ruptures more than 1000 km, leaving unbroken only the Marmara segments, to the west, and the Yedisu Segment, to the east along the main strand of the fault. To understand the palaeoseismicity of the Yedisu Seismic Gap, we undertook trench investigations close to the village of Balaban Sar?kaya, on the western part of the Yedisu Segment. We found evidence for at least five surface faulting earthquakes, from which only two are correlated with the 18 July 1784 CE and 27 June 1583 CE historical events. Although the surface rupture of the 1784 CE was reported by other trench studies, the evidence of 1583 CE event is presented for the first time. In consideration with other historical earthquakes, affecting the region east of Erzincan, we suggest that this particular section of the North Anatolian Fault may be in a seismically quiescent period, following a cluster of earthquakes in its near history. In order to test this hypothesis, further studies are needed to increase our knowledge on the temporal and spatial seismic behaviour of the Yedisu Segment, which has potential to create an earthquake with M _w ~7.2 in the near future.     

Determination of snow water equivalent over the eastern part of Turkey using passive microwave data

Information on regional snow water equivalent (SWE) is required for the management of water generated from snowmelt. Modeling of SWE in the mountainous regions of eastern Turkey, one of the major headwaters of Euphrates–Tigris basin, has significant importance in forecasting snowmelt discharge, especially for optimum water usage. An assimilation process to produce daily SWE maps is developed based on Helsinki University of Technology (HUT) model and AMSR‐E passive microwave data. The characteristics of the HUT emission model are analyzed in depth and discussed with respect to the extinction coefficient function. A new extinction coefficient function for the HUT model is proposed to suit models for snow over mountainous areas. Performance of the modified model is checked against the original, other modified cases and ground truth data covering the 2003–2007 winter periods. A new approach to calculate grain size and density is integrated inside the developed data assimilation process. An extensive validation was successfully performed by means of snow data measured at ground stations during the 2008–2010 winter periods. The root mean square error of the data set for snow depth and SWE between January and March of the 2008–2010 periods compared with the respective AMSR‐E footprints indicated that errors for estimated snow depth and predicted SWE values were 16.92 cm and 40.91 mm, respectively, for the 3‐year period. Validation results were less satisfactory for SWE less than 75.0 mm and greater than 150.0 mm. An underestimation for SWE greater than 150 mm could not be resolved owing to the microwave signal saturation that is observed for dense snowpack. Copyright © 2012 John Wiley & Sons, Ltd.     

The statistical study of precursory anomalies observed in Chinese Seismological Network

ｎｔｒｏｄｕｃｔｉｏｎＧｅｎｅｒａｌｙｗｅｒｅｇａｒｄｔｈｅｖａｒｉａｂｌｅｐａｒｔｓｏｆｐｒｅｃｕｒｓｏｒｙｄａｔａｆｒｏｍｗｈｉｃｈｔｈｅｄｉｓｔｕｒｂａｎｃｅｓａｎｄｔｈｅｏｂｓｅｒｖａｔｉｏｎａｌｅｒｏｒｓｈａｖｅｂｅｅｎｒｅｍｏｖｅｄａｓｔ...     

Patterns of significant seismic quiescence on the Mexican Pacific coast

Many authors have proposed that the study of seismicity rates is an appropriate technique for evaluating how close a seismic gap may be to rupture. We designed an algorithm for identification of patterns of significant seismic quiescence by using the definition of seismic quiescence proposed by Schreider (1990). This algorithm shows the area of quiescence where an earthquake of great magnitude may probably occur. We have applied our algorithm to the earthquake catalog on the Mexican Pacific coast located between 14 and 21 degrees of North latitude and 94 and 106 degrees West longitude; with depths less than or equal to 60 km and magnitude greater than or equal to 4.3, which occurred from January, 1965 until December, 2014. We have found significant patterns of seismic quietude before the earthquakes of Oaxaca (November 1978, M_w = 7.8), Petatlán (March 1979, M_w = 7.6), Michoacán (September 1985, M_w = 8.0, and M_w = 7.6) and Colima (October 1995, M_w = 8.0). Fortunately, in this century earthquakes of great magnitude have not occurred in Mexico. However, we have identified well-defined seismic quiescences in the Guerrero seismic-gap, which are apparently correlated with the occurrence of silent earthquakes in 2002, 2006 and 2010 recently discovered by GPS technology.     

Precursory seismic quiescence: A preliminary assessment of the hypothesis

Numerous cases of precursory seismic quiescence have been reported in recent years. Some investigators have interpreted these observations as evidence that seismic quiescence is a somewhat reliable precursor to moderate or large earthquakes. However, because failures of the pattern to predict earthquakes may not, in general, be reported, and because numerous earthquakes are not preceded by quiescence, the validity and reliability of the quiescence precursor have not been established.We have analyzed the seismicity rate prior to, and in the source region of, 37 shallow earthquakes (M 5.3–7.0) in central California and Japan for patterns of rate fluctuation, especially precursory quiescence. Nonuniformity in rate for these pre-mainshock sequences is relatively high, and numerous intervals with significant (p<0.10) extrema in rate are observed in some of the sequences. In other sequences, however, the rate remains within normal limits up to the time of the mainshock. Overall, in terms of an observational basis for intermediate-term earthquake prediction, no evidence is found in the cases studied for a systematic, widespread or reliable pattern of quiescence prior to the mainshocks.In earthquake sequences comprising full seismic cycles for 5 sets of (M 3.7–5.1) repeat earthquakes on the San Andreas fault near Bear Valley, California, the seismicity rates are found to be uniform. A composite of the estimated rate fluctuations for the sequences, normalized to the length of the seismic cycle, reveals a weak pattern of a low rate in the first third of the cycle, and a high rate in the last few months. While these observations are qualitative, they may represent weak expressions of physical processes occurring in the source region over the seismic cycle.Re-examination of seismicity rate fluctuations in volumes along the creeping section of the San Andreas fault specified by Wyss and Burford (1985) qualitatively confirms the existence of low-rate intervals in volumes 361, 386, 382, 372 and 401. However, only the quiescence in volume 386 is found by the present study to be statistically significant.     

A 3-D numerical study of salinity variations in the Bohai Sea during the recent years

Salinity is an important component of the marine system. Previous studies indicated that the mean salinity in the Bohai Sea had increased by 2.0 psu in the second half of the 20th century, mainly due to a sharp decrease in the Yellow River runoff, and also the effects of large-scale climatic variations and the intrusions of the North Yellow Sea Water (NYSW). Since 2002, the Yellow River Conservancy Commission has carried out the flow regulation at the beginning of every flood season, resulting in more discharge of the Yellow River freshwater into the Bohai Sea. In this study, the variations of salinity in the Bohai Sea during the recent years are investigated using a well-established three-dimensional baroclinic model, HAMburg Shelf Ocean Model (HAMSOM). The simulation results show that the Yellow River diluted water was mainly discharged into the Laizhou Bay, so the remarkable increase in the Yellow River runoff after 2002 led to a regime shift of salinity in the Laizhou Bay. However, in other parts of the Bohai Sea, salinity variation was influenced by the surrounding rivers or the intrusions of NYSW, and has little relation with the Yellow River runoff. As a whole, advection is more important than diffusion in the salinity distribution, and seasonal oscillation is the main feature of salinity variation. Via several case studies, evaporation and precipitation rates are found to be important in the long-term simulation of salinity.     

西北地区东部强震前地震活动演化特征

通过对1900年以来西北地区东部10次强震前不同时间尺度的地震分布特征以及演化过程的研究表明,西北地区东部强震前大多存在以下规律: 即在震中附近存在5级以上地震空缺的长期异常特征及中小地震活动水平升高的中短期异常特征。     

Spatial variations of the 660-km discontinuity in the western Pacific subduction zones observed from CEArray triplication data

We examined the spatial variation of velocity structures around the 660-km discontinuity at the western Pacific subduction zones by waveform modeling of triplication data.Data from two deep earthquakes beneath Izu-Bonin and Northeast China are used.Both events were well recorded by a dense broadband seismic network in China (CEArray).The two events are located at approximately the same distance to the CEArray,yet significant differences are observed in their records:(1) the direct arrivals traveling above t...     

Decline of groundwater table in Beijing and recognition of seismic precursory information

This paper quantitatively analyzed groundwater table fluctuations caused by groundwater overdraft, and probed into the possibility of drawing earthquake precursory information from groundwater table variations on the background of groundwater overdraft. Main effect factors of groundwater regime in Beijing region include groundwater extraction and rainfall. The decline of groundwater table was directly related to regional groundwater overdraft. Using the method of correlation analysis, the paper analyzed the...     

成都地震台前兆观测典型干扰排除

在成都地震基准台前兆数字化观测记录中,我们挑选了三种日常工作中遇到的典型前兆观测干扰,并详细论述了这些干扰产生的原因、分析判断过程和最终排除方案,以期在地震台站日常工作中对类似问题的解决有一定的指导意义和参考价值。     

临夏台地电阻率变化与震兆现象分析

以甘肃省临夏台1981年以来的地电阻率资料为基础,利用数理统计和相关分析方法,分析该台地电阻率的变化特征,探讨EW和NS两测向之间数据的相关性,以及与大夏河流量变化的对应关系,认为该台两测向数据间具有很高的相关性,可能与区域地下介质具有较均匀的电性结构有关;分析了该区降水和地下静水位对地电阻率的影响,认为地下静水位的影响更显著.此外,探讨了临夏台地电阻率资料作为地震前兆的意义,认为该台资料对甘东南及甘青交界地区的中强地震反应敏感,以下降型破年变异常为主,呈现出震级越大,异常持续时间越长的特点.该台资料同时对甘青地区成组中强地震有所反应,显示出异常持续时间长、幅度大和恢复慢的特点.     

Long-period fluctuations observed in the ionospheric absorption variations

Summary By subsequent application of power spectrum analysis, autocorrelation analysis and fast Fourier transform (FFT) of the day- and night-time absorption values of five LF radio-paths (164 kHz, 155 kHz, 185 kHz, 218 kHz and 272 kHz) in Europe during the interval 1 June 1979–30 June 1980, fluctuations with the following basic (fundamental), commonly recurrent periods were found: 3.5–5 days and 10.5–12 days. They exist in all investigated time series, while 6- and 9-day fluctuations are observed on the northern radio-paths (185 kHz and 272 kHz). Shorterperiod oscillations are most active during autumn and especially during winter, while the longerperiod oscillation (10.5–12-day) has significant amplitudes also in summer.

---

n n¶rt;am nuu aaua nma mu, amu aaua u m maauu () ¶rt; u ¶rt;a n nu u nmu a¶rt;u ma (164 , 155 , 185 , 218 u 272 ) a¶rt; n nu¶rt; 1 u 1979–30 u 1980. u a¶rt; ¶rt;u (¶rt;ama) nmu nu¶rt;: 3.5–5 ¶rt; u 10.5–12 ¶rt. u nummm u¶rt;a ¶rt;a. 6- u 9-m au a¶rt;am m a¶rt;umaa (185 u 272 ). ama au a amu u u u. ¶rt;nu¶rt; (10.5–12 ¶rt;) um aum anum¶rt; u m.

     

近50年中国东南地区地面太阳辐射变化对气温变化的影响

太阳是地球表层的最终能量来源,地面太阳辐射的变化会深刻影响地球的气候变化.本文利用中国东南地区14个气象台站1961～2008年总辐射和气温的同步观测资料,分析了近50年该地区地面太阳辐射的变化对气温变化的可能影响.结果表明,1961～1989年期间,该地区的地面太阳辐射显著减弱,所引起的气温下降超过了其他因素的增温效...     

A sequence of seismic activity in the Kanto area precursory to the 1923 Kanto earthquake

The Kanto earthquake (M=7.9) that occurred along the Sagami Trough in the Sagami Bay on 1 September 1923 was one of the most disastrous earthquakes in Japanese history. The Kanto area includes Metropolitan Tokyo and Yokohama which are densely populated, and hence it has been a matter of great concern, from the viewpoints of earthquake prediction and disaster prevention, whether or not the 1923 Kanto earthquake was preceded by precursory seismicity. A study using the most complete lists of earthquakes catalogued recently by Utsu and the Japan Meteorological Agency reveals that seismic activity in the Kanto area was appreciably higher before and after the Kanto earthquake, and that the Kanto earthquake was preceded by a sequence of anomalous seismic activity, quiescence, and foreshocks. Such higher activity before and after the Kanto earthquake is contrasted with low seismicity during the recent 30-year period. A model is proposed to explain the precursory seismic activity, subsequent quiescence, and foreshocks for the Kanto earthquake. In the model, the transition from precursory seismic activity to quiescence is ascribed to time-dependent fracture due to stress-aided corrosion. Foreshocks are related to an acceleration of premonitory slip shortly before the mainshock slip.     

Attenuation modeling of recent earthquakes in Turkey

This paper deals with the derivation of a consistent set of empiricalattenuation relationships for predicting free-field horizontal components ofpeak ground acceleration (PGA) and 5 percent damped pseudoacceleration response spectra (PSA) from 47 strong ground motion recordsrecorded in Turkey. The relationships for Turkey were derived in similarform to those previously developed by Boore et al. (1997) for shallowearthquakes in western North America. The used database was compiledfor earthquakes in Turkey with moment magnitudes (M_w) = 5 thatoccurred between 1976–1999, and consisted of horizontal peak groundacceleration and 5 percent damped response spectra of accelerogramsrecorded on three different site conditions classified as rock, soil and softsoil. The empirical equations for predicting strong ground motion weretypically fit to the strong motion data set by applying nonlinear regressionanalysis according to both random horizontal components and maximumhorizontal components. Comparisons of the results show that groundmotion relations for earthquakes in one region cannot be simply modifiedfor use in engineering analyses in another region. Our results, patternedafter the Boore et al. expressions and dominated by the Kocaeli andDüzce events in 1999, appear to underestimate predictions based ontheir curves for up to about 15 km. For larger distances the reverse holds.     

保证地震前兆数字化设备正常运转的条件和方法

"九·五"期间,陕西省地震局对周至深井进行了数字化改造。该项目于2001年底通过验收,于2002年元月开始投入正式运行。从正式观测至今,周至深井的数字化公用设备一直正常运转,保持着近100%的运行率。笔者认为,保证前兆数字化观测设备正常运转,要有可靠的接地系统,合理的供电系统,高度的工作责任心,较强的工作技能等。