Progress in Earthquake Science and Technology in China: Review and Prospects (Ⅰ)

In the article the author looks back the hard development course and great progress in earth quake science and technology in China during the last near a half of century and expounds the following 3 aspects: (1) The strong desire of the whole society to mitigate seismic disasters and reduce the effect of earthquakes on social-economic live is a great driving force to push forward the development of earthquake science and technology in China; (2) To better ensure people‘ s life and property, sustainable economic development, and social stability is an essential purpose to drive the development of earthquake science and technology in China; and (3) To insist on the dialectical connection of setup of technical system for seismic monitoring with the scientific research of earthquakes and to better handle the relation between crucial task, current scientif ic level, and the feasibility are the important principles to advance the earthquake science and technology in China. Some success and many setbacks in earthquake disaster mitigation consistently enrich our knowledge regarding the complexity of the conditions for earthquake occurrence and the process of earthquake preparation, promote the reconstruction and modernization of technical system for earthquake monitoring, and deepen the scientific research of earthquakes. During the last 5 years, the improvement and modernization of technical system for earthquake monitoring have clearly provided the technical support to study and practice of earthquake prediction and pre caution, give prominence to key problems and broaden the field of scientific research of earth quakes. These have enabled us to get some new recognition of the conditions for earthquake oc currence and process of earthquake preparation, characteristics of seismic disaster, and mecha nism for earthquake generation in China‘s continent. The progress we have made not only en courages us to enhance the effectiveness of earthquake disaster mitigation, but also provides a basis for accelerating further development of earthquake science and technology in China in the new century, especially in the 10th five-year plan. Based on the history reviewed, the author sets forth a general requirement for develop ment of earthquake science and technology in China and brings out 10 aspects to be stressed and strengthened at present and in the future. These are: upgrade and setup of the network of digitized seismic observation; upgrade and setup of the network for observation of seismic pre cursors; setup of the network for observation of strong motion; setup of the laboratories for ex periment on seismic regime; establishment of technical system for seismic information, emer gency command and urgent rescue; research on short-term and imminent earthquake predic tion; research on intermediate- and long-term earthquake prediction; research on attenuation of seismic ground motion, mechanism for seismic disaster, and control on seismic disaster; ba sic research fields related to seismology and geoscience. We expect that these efforts will signifi cantly elevate the level of earthquake science and technology in China to the advanced interna tional level, improve theories, techniques, and methods for earthquake precaution and predic tion, and enhance the effectiveness of earthquake disaster mitigation.     

Age estimates of coastal terraces in the Andaman and Nicobar Islands and their tectonic implications

The great Indian Ocean earthquake of December 26, 2004 caused significant vertical changes in its rupture zone. About 800 km of the rupture is along the Andaman and Nicobar Islands, which forms the outer arc ridge of the subduction zone. Coseismic deformation along the exposed land could be observed as uplift/subsidence. Here we analyze the morphological features along the coast of the Andaman and Nicobar Islands, in an effort to reconstruct the past tectonics, taking cues from the coseismic effects. We obtained radiocarbon dates from coastal terraces of the island belt and used them to compute uplift rates, which vary from 1.33 mm yr^− 1 in the Little Andaman to 2.80 mm yr^− 1 in South Andaman and 2.45 mm yr^− 1 in the North Andaman. Our radiocarbon dates converge on  600 yr and  1000 yr old coastal uplifts, which we attribute to the level changes due to two major previous subduction earthquakes in the region.     

1990年12月14日台湾强震的预报判据

本文运用福建省沿海气象要素的异常变化,作台湾省的中、短期地震预报,取得了成功的效果。采用长乐历年各月14时最低气压的距平值,作台湾省未来4～7个月内出现强震的预报依据,并采用热异常进行短临跟踪。当秋冬季节连续4d 长乐、福州、台北的气温均比广州累计高出10℃时,预报未来1～5d 台湾省出现7级强震。又根据近百年来台湾发生的强震,统计其活动季节,得到近20年来7级地震发生的时间,绝大部分在9～12月。     

Changes in hydrogeological properties of the River Choushui alluvial fan aquifer due to the 1999 Chi-Chi earthquake, Taiwan

Changes in hydrogeological properties of the River Choushui alluvial fan aquifer before and after the 1999 Chi-Chi earthquake, Taiwan, have been identified using pumping tests. Three wells, SH2, YL2 and SC2, located in a compressional zone with high coseismic groundwater levels, were tested. The threshold of the aquifer deformation with respect to transmissivity (T) is greater than that with respect to storage coefficient (S). Decreases in the post-earthquake S are approximately 60% at SH2 and SC2, indicating aquifer compression after the Chi-Chi earthquake. Changes in the post-earthquake T range from 61% increase to 0.8% decrease. Moreover, results from anisotropy analysis of T at SC2 further illustrate that normal stresses induced by the Chi-Chi earthquake have consolidated soil particles. Soil particles dilated laterally after the earthquake, resulting in an increase of the equivalent T. The changes in hydrogeological properties have a considerable influence on spatiotemporal fluid pressure and horizontal groundwater movement, resulting in different amounts of drawdown during post-earthquake pumping.     

新疆地震预报研究

新疆的地震预报是1970年开始的。二十多年来在“边观测、边研究、边预报”、“多路探索、多兵种联合作战”、“走综合预报之路”的方针指导下取得了长足的进展。建设了43个地震台站,投入189套仪器,建成了遍布全疆的地震无线通讯网,开展了历史地震调查和地震烈度区划工作,建立健全了地震会商预报制度,进行了多方面的地震预报研究。实际地震预报统计分析表明,扣除自然发震概率之后,趋势预报的成功率约0.3,短临预报的成功率约0.1。在前兆台网控制范围内取得了一些震例,说明地震确实是有前兆的,但又是非常复杂的。地震预报作为科学难题还有漫长的路要走。作者简要地讨论了地震观测的间接性和地震异常的离散性、难以区别的地震异常和地壳变动异常、建立在复杂现象基础上的地震前兆以及地震的混沌性对地震预报的影响等科学问题。     

Earthquake hazard of the northern parts of the Bohemian Massif and Western Carpathians

The new procedure of earthquake hazard evaluation developed by Kijko and Sellevoll is tested and applied for the border region of Czechoslovakia and Poland. The new method differs from the conventional approach. It incorporates the uncertainty of earthquake magnitudes, and accepts mixed data containing only large historical events and recent, complete catalogues. Seismic hazard has been calculated for nine regions determined in the border area. In the investigated area, data of historical catalogues are uncertain or, in many cases, the epicentral intensities are unknown. Thus, a number of assumptions have to be adopted in data preparation of catalogues since the year 1200. The calculated values of parameters b in the Gutenberg-Richter frequency-intensity relation as well as the return periods, seem to be reasonable and are generally confirmed by the results obtained from catalogues for the last 80–130 years.     

1786年康定地震形变特征的初步研究

本文对鲜水河断裂带南东段,康定断裂地震的形变带进行了分析。认为,地震形变带主要由发育于地形斜坡上的线性坡中槽或垄岗组成。形变带具分段特点,单条长850—1500米,呈右阶“斜列式”展布,中段(极震区)一带为现状型。其中的破裂面具正断兼扭动特点。空间特征上,坡中槽一侧的交替上升变化是依次、轮换出现的,它是地震断层运动屈曲作用(Fault buckling)导致地表变形的反映。这种形变现象与该带北西段(炉霍段)走滑型地震的形变带相比有明显的差异,也表明鲜水河断裂带北西、南东两段的地震破裂方式是不尽相同的,它为同一走滑带不同地段运动特征的差异提供了证据。     

FS方法及其在综合多项震兆中的应用

本文提出了一种模式识别方法--FS方法.该方法的特征取为某些论域上的模糊子集.先以每三个原始特征组成子分类器的特征集,“训练”这些分类器,然后对子分类器进行筛选,最后用筛选出的子分类器的“软”分类结果的加权平均作为判别函数,形成总的分类决策.将FS方法应用于综合多项震兆,并进行了一系列控制试验,还与地震学中几种常用的方法进行了对比试验.结果表明,FS方法是稳定和有效的.     

Quaternary tectonic faulting in the Eastern United States

Paleoseismological study of geologic features thought to result from Quaternary tectonic faulting can characterize the frequencies and sizes of large prehistoric and historical earthquakes, thereby improving the accuracy and precision of seismic-hazard assessments. Greater accuracy and precision can reduce the likelihood of both underprotection and unnecessary design and construction costs. Published studies proposed Quaternary tectonic faulting at 31 faults, folds, seismic zones, and fields of earthquake-induced liquefaction phenomena in the Appalachian Mountains and Coastal Plain. Of the 31 features, seven are of known origin. Four of the seven have nontectonic origins and the other three features are liquefaction fields caused by moderate to large historical and Holocene earthquakes in coastal South Carolina, including Charleston; the Central Virginia Seismic Zone; and the Newbury, Massachusetts, area. However, the causal faults of the three liquefaction fields remain unclear. Charleston has the highest hazard because of large Holocene earthquakes in that area, but the hazard is highly uncertain because the earthquakes are uncertainly located.Of the 31 features, the remaining 24 are of uncertain origin. They require additional work before they can be clearly attributed either to Quaternary tectonic faulting or to nontectonic causes. Of these 24, 14 features, most of them faults, have little or no published geologic evidence of Quaternary tectonic faulting that could indicate the likely occurrence of earthquakes larger than those observed historically. Three more features of the 24 were suggested to have had Quaternary tectonic faulting, but paleoseismological and other studies of them found no evidence of large prehistoric earthquakes. The final seven features of uncertain origin require further examination because all seven are in or near urban areas. They are the Moodus Seismic Zone (Hartford, Connecticut), Dobbs Ferry fault zone and Mosholu fault (New York City), Lancaster Seismic Zone and the epicenter of the shallow Cacoosing Valley earthquake (Lancaster and Reading, Pennsylvania), Kingston fault (central New Jersey between New York and Philadelphia), and Everona fault-Mountain Run fault zone (Washington, D.C., and Arlington and Alexandria, Virginia).     

Increasing critical sensitivity of the Load/Unload Response Ratio before large earthquakes with identified stress accumulation pattern

The Load/Unload Response Ratio (LURR) method is proposed for short-to-intermediate-term earthquake prediction [Yin, X.C., Chen, X.Z., Song, Z.P., Yin, C., 1995. A New Approach to Earthquake Prediction — The Load/Unload Response Ratio (LURR) Theory, Pure Appl. Geophys., 145, 701–715]. This method is based on measuring the ratio between Benioff strains released during the time periods of loading and unloading, corresponding to the Coulomb Failure Stress change induced by Earth tides on optimally oriented faults. According to the method, the LURR time series usually climb to an anomalously high peak prior to occurrence of a large earthquake. Previous studies have indicated that the size of critical seismogenic region selected for LURR measurements has great influence on the evaluation of LURR. In this study, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. The Coulomb stress change before a hypothetical earthquake is calculated based on a simple back-slip dislocation model of the event. This new algorithm, by combining the LURR method with our choice of identified area with increased Coulomb stress, is devised to improve the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. Retrospective tests of this algorithm on four large earthquakes occurred in California over the last two decades show remarkable enhancement of the LURR precursory anomalies. For some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods, significant anomalies are found if circular areas are used, and are not found if increased Coulomb stress areas are used for LURR data selection. The unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events.