天山中段2次6级地震前钻孔应变高频异常分析

2014年以来,天山中段分量钻孔应变仪空前增多,这些高采样率的应变观测资料蕴含着丰富的构造信息。如何从高采样率观测资料中提取有效的前兆异常信息,是分析研究人员亟待解决的问题。文章通过对天山中段分量钻孔应变观测数据进行S变换和超限率分析发现,在天山中段2次6级地震前有5套应变资料出现高频信息异常。这些异常均在震前出现,随后达到峰值,临震前或地震后衰减,其中短周期异常信号主要集中在10～720 min频段,且S变换与超限率分析结果具有很好的同步性。结合精河地震震源区及附近的GPS分析结果,发现高频异常信息的分布与该地区地壳运动场具有很好的一致性,进一步验证了高频信息异常的可信度。     

A 100 m laser strainmeter system installed in a 1 km deep tunnel at Kamioka, Gifu, Japan

We have installed a laser strainmeter system in a deep tunnel about 1,000 m below the ground surface at Kamioka, Gifu, Japan. The system consists of three types of independent interferometers: (1) an EW linear strainmeter of the Michelson type with unequal arms, (2) an NS-EW differential strainmeter of the Michelson type with equal arms and (3) a NS absolute strainmeter of the Fabry–Perot type. These are configured in L-shaped vacuum pipes, each of which has a length of 100 m. (1) and (2) are highly sensitive (order of 10⁻¹³ strain) and have wide dynamical range (10⁻¹³–10⁻⁶). Observations with strainmeters (1) and (2) started on June 11, 2003. (3) is a new device for absolute-length measurements of the order of 10⁻⁹ of a long-baseline (100 m) Fabry–Perot cavity by the use of phase-modulated light. This third strainmeter will be ready for operation before the end of 2004. The laser source of strainmeters (1) and (2) is a frequency-doubled YAG laser with a wavelength of 532 nm. The laser frequency is locked onto an iodine absorption line and a stability of 2 × 10⁻¹³ is attained. The light paths of the laser strainmeter system are enclosed in SUS304 stainless steel pipes. The inside pressure is kept to be 10⁻⁴ Pa. Consequently, quantitative measurement of crustal strains of the order of 10⁻¹³ can be attained by employing the laser strainmeter system of (1) and (2) at Kamioka. This resolving power corresponds to that of a superconducting gravimeter. Using the laser strainmeter system, we expect to determine parameters related to fluid core resonance, core modes and core undertone as well as other geodynamic signals such as slow strain changes caused by silent earthquakes or slow earthquakes.     

Pendulum-type laser strainmeter

Constructive disposition principles of the basic optical units of Michelson interferometers are used in making one-coordinate laser strainmeters of unequal-arm type.The fundamental advantages of pendulum-type laser strainmeter more than classical-type laser strainmeter are displayed.     

新疆钻孔应变异常特征及其与地震三要素关系研究

将新疆高精度钻孔应变仪１０年来观测到的应变异常划分为趋势异常、短期异常、临震异常三类，并对这三种异常的特征进行了分析总结．认为，地震三要素与应变异常参量关系密切，震级与异常量级、震中距有着确定性关系。     

Meteotsunami Manifestations in Geospheres

Izvestiya, Physics of the Solid Earth - The results of processing synchronous records from two laser strainmeters, a broadband seismograph, a laser nanobarograph, and a laser meter of hydrospheric...     

安徽省数字化形变仪器及观测资料的综合分析

从仪器运行情况,影响形变观测的主要因素,观测精度和映震能力等方面,对安徽省淮北,泾县,泗县数字化形变观测台站的监测能力进行了综合分析,得到了安徽省数字化形变前兆观测的基本情况,对安徽省形变台网观测资料的应用和未来台站建设具有一定的参考意义。     

青海钻孔应变映震效能研究

利用青海省6套YRY-4分量钻孔应变仪2007—2015年的观测资料,将该地区符合扫描范围的地震从震前异常和同震特征两方面进行研究。结果显示:湟源、德令哈分量钻孔应变差应变曲线地震前大多有短期超差异常;分量钻孔应变仪的同震响应幅度与震级、震中距都有关。同一地震,多台仪器多数情况同震响应幅度与震中距成反比,少数成正比;一般单台仪器同震响应幅度与地震震级成正比关系,震级越大同震响应幅度越大;分量钻孔应变仪的同震响应延迟时间大多与地震震中距成正比,震中距越远同震响应延迟时间越长;分量钻孔应变仪同震响应持续时间与震级基本成正比,震级越大同震持续时间越长。     

Groundwater microtemperature in earthquake regions

Microtemperature measurements of groundwater with a relative precision better than 1/1000°C have been made in several seismically active areas in Japan. The measured temperatures show clear coseismic signals as well as a correlation with atmospheric pressure. Simultaneous observations at various depths have shown that these temperature changes were not induced by simple groundwater level changes. Also, distinctive signals occurred before several earthquakes and seem to be caused by a different mechanism than the coseismic signals. The microtemperature at some observation sites shows excellent correlation with records of nearby sensitive borehole strainmeters. Simultaneous recording of microtemperature and strain has been initiated in some boreholes.     

周期气压波对地壳应变场观测影响的若干因素分析

地壳应变场常用钻孔体应变仪进行测量,而周期为几分钟到几小时的短周期气压波是影响体应变仪工作的一种长期因素.本文以Evertson等人推导的体应变短周期气压干扰模型为基础,从理论上进一步探讨了体应变气压影响系数与气压周期、岩石弹性参数和井孔深度的关系及变化规律.由于体应变观测井孔存在耦合效应,又建立了大气压垂直载荷作用下观测井孔耦合系数计算方程,比较了在多重因素作用下体应变气压影响系数理论观测值与无孔岩石真实值之间的差异,并与涞水、顺义、东三旗和昌平台的Sacks体应变实际观测资料进行了比对分析.这对地震前兆微动态信息背景场的探索具有实际意义.      

Groundwater monitoring for earthquake prediction by an amateur network in Japan

Since 1976 groundwater-levels and the temperature of thermal water have been monitored in 100 wells distributed mostly in the southern Kanto and Tokai districts of Japan in order to predict earthquakes. Good examples of groundwater precursors were recognized prior to the following destructive earthquakes: the 1978 West Off Izu-Oshima Earthquake (M 7.0), the 1978 Off Miyagi Earthquakes (M 7.4), and the 1980 East Off Izu Peninsula Earthquake (M 6.7). In the 1978 West Off Izu-Oshima Earthquake, groundwater levels and the Japan Meteorological Agency (JMA) volume strainmeters, installed in the Izu peninsula, showed precursory changes at about the same time. In the other cases, however, precursory behavior was observed only in water level and temperature monitoring. Empirical relations are given between earthquake magnitude and the epicentral distance of the farthest groundwater anomaly, and between earthquake magnitude and the precursor time of groundwater.     

The study of synchronously measured variations in the Earth’s surface strain and groundwater level

Correlated variations in the surface strain, atmospheric pressure, and groundwater level are studied at two points about 40 km apart in an aseismic region. Comparative analysis of the results obtained by laser strainmeters with bases of 10 and 300 m and pressure gage sensors of the water level in boreholes 400–1000 m deep and the atmospheric pressure with a resolution of 0.03 mbar is carried out. The estimates of barometric coefficients obtained from the data of spaced sensors of different types revealed a number of specific features of dynamic interactions in the Earth’s crust-hydrosphere-atmosphere system. The space-time scales of disturbances, the velocity of their propagation, and the seasonal variations in the estimated coefficients are found.     

1976年唐山地震前土层水平最大剪应变的时空分布

土层应变仪观测网的观测结果表明:土层水平最大剪应变在唐山地震前有异常,异常后便发生了主震;异常时间等值线从震中向外围传播,其传播速度为每天0.1—6.6公里,从震中区向外围加快,以沿着通过唐山主震震中区的北东和北西向断裂带的传播速度为最快;最高等值线圈闭震中或在震中附近     

Generalization of the results of long-term strainmeter and GPS observations for intraplate regions

The measurements of contemporary deformations in Asia in the region of active seismic processes stretching from Northern Tien Shan through Altai and Sayan Mountains to Lake Baikal have been carried out for a few decades by strainmeters and tiltmeters. Recently, these works were expanded by the network measurements by the methods of space geodesy. Studying the contemporary displacements and deformations of the Earth’s crust is necessary for solving various problems on a wide range of spatial and time scales from exploring the contemporary deformations of the tectonic plates and present-day seismicity to estimating the man-made loads on the geological medium. The measurements of the deformations are conducted by different methods with short and long baselines, on the surface and at different depths. Based on the obtained data, it is possible to analyze the strain rates at different frequencies and to compare them with the level of seismic activity in the region. In recent decades, the seismic zone located in the south of the Siberian platforms experienced a few strong (M = 6.3–7.5) earthquakes, during which the deformation and displacement fields were captured. South of this region, the displacement fields during the earthquakes with the magnitude above 8 were recorded by the space geodetic methods in China. By excluding the coseismic effects, one can estimate the tectonic component of the displacements and deformations.     

钻孔差应变仪观测的苏门答腊大地震激发的地球环型自由振荡

我们率先用钻孔应变仪观测资料研究了地球自由振荡. 泰安地震台有差应变和体应变两种钻孔应变观测仪器，都观测到2004年12月26日苏门答腊大地震激发的地球自由振荡. 体应变仪观测到地球的球型振荡，而差应变仪观测到地球的环型振荡. 两种观测还记录到环型振荡与球型振荡相互的耦合作用. 观测也记录到明显的一些振型的谱线分裂现象. 用直接观测到的高质量的环型振荡资料求解了0T8～0T19等主要振型的Q值. 根据两个方向的剪应变观测数据，求解了环型振荡的最大剪应变方向，发现这个方向是相当稳定的. 这种研究表明，高精度钻孔应变观测仪是一种理想的地壳形变观测仪器，可以为地球自由振荡研究提供更丰富的信息.     

Toroidal free oscillations of the Earth observed by a ring laser system: a comparative study

In this study, we explore the potential of measuring systematically the Earth's free oscillations using ring laser gyro (RLG) vertical axis rotational records. The RLG that we use is the vertical axis G-ring laser system of the Geodetic Observatory Wettzell (Germany). In 2009, its signal-to-noise ratio was considerably improved over the broadband frequency range of seismic measurements. Since then, three large magnitude earthquakes have occurred (Samoa Islands 2009; Maule, Chile, 2010; and Tohoku, Japan, 2011), leading to the first direct observations of rotational ground motions induced by toroidal free oscillations of the Earth. We compare these G-ring laser observations with synthetic seismograms computed by summing normal modes. We also analyse amplitude spectra of real and synthetic data to aid in the interpretation of the observations. We show that several toroidal modes are detected by the G-ring laser for earthquakes with a moment magnitude M _W????8.0 and that our observations are in reasonable agreement with the synthetic spectra. We also report evidence for mode coupling in both translation and rotation spectra.     

地壳应变场观测中体应变与面应变转换系数的计算

将钻孔体应变仪与分量式应变仪的观测资料在面应变平台上进行整合,对于解决目前两种应变仪观测数据的评估、分析、处理和地震预报问题有实际意义．根据潘立宙-陈沅俊和Evertson理论及弹性力学知识,分别建立了平面应力作用下体应变和面应变观测的力学模型,推导了观测钻孔、空孔和无孔岩石体应变与面应变转换系数的计算公式,发现它们都可以归结为同一公式描述,差异仅在于k（体应变仪钢筒内壁或无孔岩石面应变与空孔岩石面应变之比）的取值不同．用Evertson理论推导的公式与空孔岩石情形相近,当岩石弹性模量为4times;1010——8times;1010 Pa时,二者都可以看成是对潘-陈公式的一种简化、近似计算;无孔岩石的情况则相当于在岩石弹性模量为1times;1010 Pa时对该式的一种估计. 文中结合实际情况对转换系数的各种影响因素进行了详细分析．      

The strain seismograms of P- and S-waves of a local event recorded by four-gauge borehole strainmeter

At a sampling rate of 100 samples per second,the YRY-4 four-gauge borehole strainmeters(FGBS) are capable of recording transient strains caused by seismic waves such as P and S waves or strain seismograms. At such a high sampling rate, data from the YRY-4 strainmeters demonstrate fairly satisfactory self-consistency. The strain tensor seismograms demonstrate the senses of motion of P waves, that is, the type of seismic wave travels in the direction of the maximum normal strain change. The observed strain patterns of S waves significantly differ from those of P waves and should contain information about the source mechanism. Spectrum analysis shows that the strain seismograms are consistent with conventional broadband seismograms from the same site.     

四分量钻孔应变观测的实地绝对标定

钻孔应变观测的实地标定问题有二层涵义: 在第一个层面上, 可以认为实地标定是相对室内标定而言的, 是对仪器(元件)灵敏度的标定, 称为相对标定; 在第二个层面上, 由测值换算出孔径相对变化以后, 还要利用理论固体潮等依据对与钻孔周围介质的弹性有关的参数进行标定, 从而给出应变变化, 称为绝对标定。 文中提出了四分量钻孔应变观测的绝对标定的新方法, 并以昌平台RZB-1型钻孔应变观测为例进行实际应用, 取得了相当好的结果。     

Optical Fiber Interferometers for Referencing Surface Benchmarks to Depth

—We have developed and operated optical fiber interferometers for monitoring displace ments within boreholes, as part of a program of crustal deformation measurement. These optical fiber strainmeters—a total of twelve instruments at two sites in southern California—were installed to sense the motion of the end-monuments of much longer baseline strainmeters and tiltmeters, allowing correction for any near-surface ground movement. One of the installations was specifically designed to investigate the distribution of deformation with depth, measuring over several borehole length-intervals from 5 m to 50 m. The displacements recorded over year-long time scales along these length intervals range up to 6 mm and show internal consistency and stability at the 50 μ m level. The use of these interferometers to provide correction signals for kilometer-scale crustal strain measurements has resulted in greatly improved records.