ISC业务考察报告

前言我们于1982年1月18日至20日在英国国际地震中心ISC考察了三天。现任主任休斯先生(A.A.Hughes)详细地讲述了ISC的全球地震资料收集、汇编、出版的工作流程。我们就工作流程中使用的方法、环节、处理、设备等等约一百多个问题,进行了讨论。了解、学习ISC地震资料汇编的全貌和特点。有助于改进我们地震资料的汇编工作。我国自1979年加入ISC以来。每月按时向它提供19个基准地震台地震资料。这些资料是由国家地震局地球物理所九室汇编成地震月报,然后经专人抄写成ISC的格式化数据表     

ISC地震观测报告的日常产出

以ISCloc为核心方法和技术,ISC统一分析处理全球的观测数据并定期出版地震观测报告。从资料收集、数据关联、定位方法和技术、数据分析与出版4个方面阐述ISC观测报告产出的主要过程。2008年后,ISC每年汇集300 000—500 000次以上地震,其中约20%的地震需要地震学家分析和审核,观测报告发布、出版时间比实际地震发生时间滞后约24个月。     

国际地震中心(ISC)

国际地震中心(ISC)在联合国教科文组织(UNESCO)资助下于1964年成立。作为国际地震目录(ISS)的延续,该中心紧跟John Milne教授和Harold Jeffreys爵士的开创性工作,在世界范围内与其他地震数据中心和其他地震机构合作,收集、整理和分析地震事件,以提高对地震科学知识和地球结构的认识。本文对ISC基本概况、数据来源和数据服务等进行了介绍。     

国际地震中心(ISC)2009—2011发展战略

引言 本文确定了国际地震中心（ISC）的下一步发展战略。它经ISC执行委员会在2008年6月8-9日萨彻姆（Thatcham）会议上考虑并获得支持。ISC理事会在2009年1月11日开普敦（Cape Town）会议期间原则上批准了此战略规划。规划中还对ISC理事会成员在会后一个月内提交的校正／修改意见予以考虑。     

ISC地震震级测定工作目前情况及建议之改进

ISC的主要目的是科学研究,但在它的章程中曾特别提到用它之资料来帮忙研究地震活动性,地震灾害之减轻及地震预报。这种研究之后果不仅是有科学意义,并且对可能发生地震的地区内地震危险性之减小,人民之安全皆有重大关系。外界机关,例如保险公司,工程建筑公司等愈来愈乐于使用ISC的地震历史档案,这也是ISC设立团体会员(资格)的一个主要理由,这些团体会员也向ISC提供了额外的基金并希望ISC之工作有所改进。 ISC之地震历史档案常常用来找查某个地区之地震情况;此档案中仅包括有1463年以后的地震之“主估算(计算)结果”。这些主计算结果是当收集到足够地资料之后     

国际地震中心(ISC)简介

地震是一种灾害性的自然现象,它的发生是不受国界的限制的。因此地震必须由很多国家共同记录,并相互交换资料,才能研究透彻。现在国际上有个重要的地震资料交换机构,即国际地震中心,简称ISC,它是一个非官方组织,由许多国家的学术团体或事业机构所资助而工作。任务是从全球地震台收集资料,把它重新加以分析和计算,并把结果印成月报和区域地震目录,供全球的地震学者或机构使用。 ISC之历史——19世纪末叶有个英国人名叫John Milne在日本制造了Milne式地震仪并研究地震。那时人们就感到,必须     

国际地震中心(ISC)简介

纽伯里(Newbury)是一个只有两万五千人口小的城市,美丽而又安静,它座落在伦敦的西边约100公里的地方。著名的国际地震中心ISC(International SeismologicalCentre)就设在这里。全世界的1000个以上地震台的资料(北至格陵兰,南至南极州)都定期送到这里,进行全球地震资料的汇集、分析和出版。国际地震中心的主要任务是收集世界范围的地震信息,包括仪器记录数据和宏观地震资料,精确地计算地震的位置和震级,编辑并出版全球地震目录、地震报告以及大地震的宏观资料,建立完整的资料档案并对有关的地震问题提供咨询服务。     

世界地震服务机构Ms值的对比

笔者利用1978—1983年的Ms资料,统计分析了PEK、ISC、MOS和NEIS四大地震服务机构报告的Ms值之间的相对偏差。以NEIS(Ms值)作为参考基准,结果表明了PEK(Ms值)平均偏高0.2级,并且发现了大陆地区比较西太平洋地震带的地震。PEK值相对有较大偏高;对于中国及其邻近的大陆地区,PEK—NEIS平均可达0.5级。这种区域差异,对于MOS也同样存在,只是程度较小一些。此外,ISC与NEIS的符合程度最好;MOS相对于ISC的系统偏差仅0.01级,但仍然存在明显的区域差异。本文对四大台网震级进行比较,并着重讨论PEK相对NEIS的偏离,以及中国及其邻近地区地震的Ms偏离情况。     

强震速报震级的比较研究

本文对比了成都速报、“中心”速报、地球所临报和 ISC报告所测定的震级 ,初步讨论了出现差异的原因     

地震数据管理文件组

前言“地震数据文件管理组”主要是为了管理地震年报和地震月报的数据。地震数据格式以子记录为单位被建立在五吋软磁盘內。一个月的地震数据就构成一个“地震数据文件”。解调数据文件可以生产地震月报的排版格式,可供影印制版印刷。编制印刷国际地震中心ISC所规定的震中参数格式数据,震相参数格式数据,作为同ISC交换地震资料使用。与此同     

Discrepancies in earthquake location between ISC and other agencies

The different operating requirements of the International Seismological Centre (ISC) from those of the National Earthquake Information Service of the US Geological Survey(NEIS), and of the prototype International Data Center to monitor the Comprehensive Test Ban Treaty (pIDC), result in some discrepancies between earthquake locations computed by the three agencies. For larger events recorded by many stations the differences are small, but for some smaller events differences in location of up to 20^° may occur. The largest discrepancies are found for small events in areas where later analysis by ISC has the benefit of additional readings from regional seismograph networks and where ISC has made a different interpretation of the station readingsavailable to pIDC and NEIS. We identify regions where such discrepancies occur most frequently, and give some examples for which the augmented data set of ISC has resulted in significant improvement for specific earthquakes. NEIS and, particularly, pIDC produce their results more speedily than ISC, and these form a valuable starting point for the later, more complete ISC analysis, which is commonly considered the most definitive compilation of global earthquake information.     

Updating default depths in the ISC bulletin

The International Seismological Centre (ISC) publishes the definitive global bulletin of earthquake locations. In the ISC bulletin, we aim to obtain a free depth, but often this is not possible. Subsequently, the first option is to obtain a depth derived from depth phases. If depth phases are not available, we then use the reported depth from a reputable local agency. Finally, as a last resort, we set a default depth.In the past, common depths of 10, 33, or multiples of 50 km have been assigned. Assigning a more meaningful default depth, specific to a seismic region will increase the consistency of earthquake locations within the ISC bulletin and allow the ISC to publish better positions and magnitude estimates. It will also improve the association of reported secondary arrivals to corresponding seismic events.We aim to produce a global set of default depths, based on a typical depth for each area, from well-constrained events in the ISC bulletin or where depth could be constrained using a consistent set of depth phase arrivals provided by a number of different reporters.In certain areas, we must resort to using other assumptions. For these cases, we use a global crustal model (Crust2.0) to set default depths to half the thickness of the crust.     

A scheme to set preferred magnitudes in the ISC Bulletin

One of the main purposes of the International Seismological Centre (ISC) is to collect, integrate and reprocess seismic bulletins provided by agencies around the world in order to produce the ISC Bulletin. This is regarded as the most comprehensive bulletin of the Earth’s seismicity, and its production is based on a unique cooperation in the seismological community that allows the ISC to complement the work of seismological agencies operating at global and/or local-regional scale. In addition, by using the seismic wave measurements provided by reporting agencies, the ISC computes, where possible, its own event locations and magnitudes such as short-period body wave m _b and surface wave M _S . Therefore, the ISC Bulletin contains the results of the reporting agencies as well as the ISC own solutions. Among the most used seismic event parameters listed in seismological bulletins, the event magnitude is of particular importance for characterizing a seismic event. The selection of a magnitude value (or multiple ones) for various research purposes or practical applications is not always a straightforward task for users of the ISC Bulletin and related products since a multitude of magnitude types is currently computed by seismological agencies (sometimes using different standards for the same magnitude type). Here, we describe a scheme that we intend to implement in routine ISC operations to mark the preferred magnitudes in order to help ISC users in the selection of events with magnitudes of their interest.     

Results of locating the IASPEI GT(0-5) reference events using the standard ISC procedures

The International Seismological Centre (ISC) is charged with production of the definitive global bulletin of seismic events, based on the most comprehensive set of parametric data collected from all over the world. Almost every event in the bulletin retains the original hypocentral solutions reported to the ISC by contributing agencies. In addition, where possible, the ISC computes its own solution, which is intended to be the most accurate where the data from several networks are used. It is because of the requirement for consistency of the bulletin over the years that the procedures used at the centre to compute hypocentres have remained rather conservative despite considerable advances made in the field of earthquake location.The ISC has developed and put into operation a new data management system. As a result, it is now possible to review and subsequently introduce more up-to-date methods of locating seismic events into the operations. The ISC Governing Council called for a workshop dedicated to location procedures, which was held during the 2005 IASPEI General Assembly in Santiago, Chile.To compare the accuracy of different location algorithms, a list of 156 reference events (IWREF) was selected prior to the workshop. The list includes geographically well distributed earthquakes and explosions with positions known with an accuracy of up to 5 km. It covers the period of 1954-2001 and includes all station readings and hypocentral solutions of different agencies available for these events in the ISC bulletin. Although the original ISC solutions are included, these may be different from the solution obtainable now due to changes in the ISC procedures over the years. This paper presents the results of relocation of these events using standard ISC location procedures as of 2005. These new ISC locations and analysis of their shifts with respect to reference locations present a benchmark for further improvement.     

Estimation of PKP times from ISC data

The International Seismological Centre (ISC) treats reports of the earliest observed core phase arrivals from earthquakes as PKIKP observations and provides residuals based on Jeffreys-Bullen PKIKP times. An analysis of some 30 000 such data from ISC bulletins for the year 1967 has shown that the data include, in addition to PKIKP, many observations of PKP₁ and precursors to PKP. By the use of simple truncation and trimming techniques, travel-time curves (expressed as differences from JB), with standard errors, have been obtained for PKIKP in the ranges 110 to 139° and 152 to 173°, and for PKP₁ in the range 144 to 154°. The PKIKP curve in these ranges agrees quite closely with the curve obtained by Cleary and Hales, and with one derived from model 1066B of Gilbert and Dziewonski, except that the Cleary-Hales curve is up to 0.7 s earlier at distances below 120°, and the 1066B curve is up to 1 s later beyond 152°. The PKP₁ curve is in good agreement with that derived from 1066B.A plot of the number of observations in each 1° distance interval has been used to estimate the positions of the cusps B, C and D on the PKP curve as 144, 152.5 and 115°, again in reasonable agreement with 1066B.     

Variations with time in the detection thresholds of P for seismological stations reporting to the ISC

To determine maximum-likelihood magnitudes for a given seismological network requires estimates of the detection thresholds of short-period P for the individual stations. Ideally the detection threshold of a station with fixed instrumentation and operating procedures would be constant. However, some stations reporting to the International Seismological Centre (ISC) show systematic variations with time. Other stations are unreliable or report amplitudes (A) and periods (T) only intermittently. Ways are therefore needed for choosing stations that have a consistent performance over many years. Two rough measures are described here that can be used to look at variation in the apparent detection thresholds with time: one is the number of A/T observations (at distances greater than 20^∘) and the other , for the P detections associated each month by the ISC; being the average . Some of the factors that control detection thresholds and clearly revealed by these rough measures are: array stations have lower thresholds than conventional observatories; installation of automatic detectors can lower the threshold; and annual variations in noise level are reflected in annual variations in detection thresholds. For some stations an apparent lowering of the threshold appears not to be due to changes at the station, but is a consequence of the lowering of the ISC reporting thresholds in the region around the station. For stations of the Swiss seismological network there is a slow rise in the threshold from the mid-1970s to 1992 which is difficult to explain but seems to be due to a gradual changes in the detail with which the seismograms are analysed.     

The location and mislocation of subcrustal earthquakes

In regions, such as subduction zones, with systematic velocity variations from the travel-time model, the estimated hypocentres may be significantly mislocated and the estimated hypocentres may depend strongly on the stations and phases used. The estimated depths of earthquakes beneath the North Island, New Zealand, as determined by the International Seismological Centre and the New Zealand Seismological Observatory are used to illustrate this effect. Compared with ISC depths determined using local P phases only, the NZSO depths using local P and S phases are shallower by about 15 km while ISC depths using local and releseismic P phases are shallower again by about 30 km (and up to 70 km). Thus ISC depths which do not use teleseismic observations are not consistent with those which do and so care must be exercised when using both types of solution.     

Effect of leaf distribution pattern on the interception storage capacity of leaf litter under simulated rainfall conditions

Rainwater interception by leaf litter is an important part of forest hydrological processes. The objective of this study was to investigate the interception storage capacity (ISC) of woodland leaf litter for three leaf distribution patterns, one flow path, two flow paths, and three flow paths, manually simulated via one-by-one leaf connection in the top leaf litter layer. A random pattern served as the control. Three different slopes (0°, 5° and 25°, representing flat, gentle and steep slopes, respectively) and two contrasting leaf litters (needle-leaf litter, represented by P. massoniana leaves, and broad-leaf litter, represented by C. camphora leaves) with a biomass of 0.5 kg/m² per unit area were applied, at a rainfall intensity of 50 mm/h. Results suggested that leaf distribution pattern greatly impacts litter drainage and hence affects leaf litter ISC. The delaying capacity of litter drainage initiation and ISC of broad-leaf litter were higher than those of needle-leaf litter under the same slope conditions. The maximum ISC (C_max) and minimum ISC (C_min) of leaf litter at flat and gentle slopes were higher than those at steep slope. C_min of the broad-leaf litter was two times higher than that of needle-leaf litter on average. When raindrops reached the litter layer, some were temporarily intercepted by the top litter layer while others infiltrated leaf litter sublayer along leaf edges, and in the process, some rainwater flowed through litter layer and contributed to lateral litter drainage along the potential flow path formed by leaves. The lateral litter drainage of broad-leaf litter was higher than that of needle-leaf litter, and the partitioning of rainwater into lateral litter drainage increased with increases in slope. The difference in leaf litter C_max among different slopes and leaf shapes decreased with flow path increasing. Therefore, leaf distribution pattern notably impact leaf litter ISC, which is similar to leaf shape and slope impacts. On inclined slopes, avoiding leaf accumulation to form flow path is helpful for improving ISC.     

Extraction of soluble collagen and its feasibility in the palaeodietary research

In current palaeodietary research, gelatinization is the main method to extract insoluble collagen(ISC) from ancient bones. However, the degradation products of ISC, i.e., soluble collagen(SC), is often neglected and abandoned. In this work, we try to separate the extracts of ancient bones using gel chromatography and compare the contents of carbon and nitrogen, atomic C/N ratio, and stable carbon and nitrogen isotopic values of the extracts from three peaks to determine which peak can be attributed to SC. At last, the potential application of SC in palaeodietary research is discussed based on the comparison of stable isotopic values between ISC and SC. Among the three peaks, the second with the retention time between 17.5 min and 27.5 min had the most broad peak shape, indicating that the molecular weights of proteins collected were most variable. Besides, the contents of carbon and nitrogen and atomic C/N ratio of extracts in this peak were closest to the corresponding ISC. Based on the above, we conclude that the extract in second peak is SC. More important, the δ 13C and δ 15N values of ISC and SC are very similar. For ISC and SC with atomic C/N ratios within the normal range(2.9–3.6), the mean difference of δ 13C value was only(0.3±0.2)‰(n=2) while δ 15N value was(0.6±0.1)‰(n=2). Although the atomic C/N ratios of some SC are slightly beyond the normal range, the mean differences of δ 13C and δ 15N values were still only(0.4±0.1)‰ and(0.3±0)‰(n=2) respectively. These isotopic differences are quite below the isotope fractionation in one trophic level(δ 13C values of 1‰–1.5‰ and δ 15N values of 3‰–5‰), suggesting that SC had great application potentials in palaeodietary research.     

Earthquake detectability estimates for 478 globally distributed seismograph stations

Using the P-wave reportings to the ISC for the four years 1971–1974, the earthquake detectability for 478 globally distributed seismograph stations in individual distance interval 30–90° has been estimated in terms of the 50% incremental detection threshold expressed in ISC m_b units.