诺伊迈尔台阵及其对南大西洋和南极洲地震研究的影响

于1997年南方的夏季，在南极洲毛德皇后地西部的德国诺伊迈尔基地附近布设了一个小孔径地震台阵。小孔径台阵是监测和定位地方或区域范围内微震的重要的地震学手段。地震台阵记录优于单台记录，可以直接计算地震信号的慢度矢量。另一个优点是通过各道聚束或叠加来提高信噪比。这个台阵由15个短周期垂直向地震计组成，布设成三个同心圆，最大孔径为2km，中心地震计是三分量宽频带地震计。这个台阵沿用了现有北半球台阵的设计，如挪威的NORESS和ARCESS台阵。同时在南非新萨纳四号基地布设了一个标准宽频带地震台站(台站代号为SNAA)。1998年初，在阿根廷贝尔格拉诺二号基地(BELO)布设了另外一个地震台站，SNAA和BELO台站拓展了诺伊迈尔地震台阵的孔径，使其达到1100km。该台阵建立以来，已检测到一些发生在毛德皇后地被动陆缘的地方地震。检测到这些事件说明了该台阵具有很好的监测能力并且有助于更好地了解该地区的地质构造演化。更有意义的是，现在可以检测到南桑威奇地区的地震事件，并且定位精度也大大提高。而此前在这个地区观测到的许多地震事件在全球目录中都不曾出现。     

一次地震导致另一次地震

在本期(Nature,375卷,1995年5月18日)的221页上,Harris,Simpson和Reasenberg考察了南加州相邻地震间可能存在的联系。作者发现在一个大于等于5级地震震后的前18个月内,任一个邻近地区发生的后续大震(M≥5)几乎总是发生在一条被首震引起的静应力场变化所加载趋于破裂的断层上。如果是这样的话,它对于地震危险性评价意味着什么呢? 一次地震能够用一个弹性介质内的有限位错     

震后一分钟：强震图,有效震中和有效震级

本文报道了台湾实时地震监测的最新进展,尤其是台湾中心气象局遥测地震台网(CWBSN)的实时强震监测。该项工作旨在大震发生后迅即速报。如果速报能在强振动到来之前完成,那么地震早期警报将成为可能。CWBSN已能在大震发生后一分钟内给出强度图、震中和震级。速报和早期警报主要适用于大震(M>>5);不限幅波形记录的需要促使CWBSN在1995年将强震探测仪(如力平衡加速度计)并入其遥测地震监测系统中。将时间域递归处理应用于多道输入地震信号,通过一组联网微机生成强度图。通过等值线,能迅速识别出位于强度图最大等值线(通常为100gal)中央的有效震中。有效震级也能迅速由最大等值线(通常为100gal)覆盖的表面积确定。对于具有有限破裂面的大震,如此得出的震中和震级是更适当的震源位置和破坏强度的估算值。有效震中给出了破坏区域的中心,与传统的震中定位比较,后者仅给出了破裂形成的初始位置。有效震级所反映的更接近地震破坏的潜能,而不是强调总能量释放的传统震级。CWBSN已能在一分钟内获取上述震源的关键信息。这一时间将会进一步缩短至30s以内,如本文中举例描述的那样,地震早期警报的确是一个可能达到的目标。速报和早期警报信息将电传给用户,以采取人为或无人干予的快速反应行动。     

Estimation of groundwater residence time using the 36Cl bomb pulse

We propose a methodology for estimating the residence time of groundwater based on bomb-produced (36)Cl. Water samples were collected from 28 springs and 2 flowing wells located around Mt. Fuji, Central Japan. (36)Cl/Cl ratios in the water samples, determined by accelerator mass spectrometry (AMS), were between 43 × 10(-15) and 412 × 10(-15). A reference time series of the above-background (i.e., bomb-derived) (36)Cl concentration was constructed by linearly scaling the background-corrected Dye-3 data according to the estimated total bomb-produced (36)Cl fallout in the Mt. Fuji area. Assuming piston flow transport, estimates of residence time were obtained by comparing the measured bomb-derived (36)Cl concentrations in spring water with the reference curve. The distribution of (36)Cl-based residence times is basically consistent with that of tritium-based estimates calculated from data presented in previous studies, although the estimated residence times differ between the two tracers. This discrepancy may reflect chlorine recycling via vegetation or the relatively small change in fallout rate, approximately since 1975, which would give rise to large uncertainties in (36)Cl-based estimates of recharge for the period, approximately since 1975. Given the estimated ages for groundwater from flowing wells, dating based on a (36)Cl bomb pulse may be more reliable and sensitive for groundwater recharged before 1975, back as far as the mid-1950s.     

1995年日本中部伊东市近海震群附近一水井的弱阻尼响应

1995年,日本中部静冈县伊东市近海震群活动期间,我们观测了距震中约5km远的弱阻尼井蓄水层系的同震和非同震水位变化情况。每次水位变化都由随后为阻尼谐振的有线性趋势成分的静位移构成。这些振荡的特征频率和衰减参数分别为18.3s和0.024s~(-1)。震群活动期间,我们在8天内检测到了14次这种事件。位移值几乎都是2 mm或更小,只有两次例外,其位移值分别为4mm和6 mm。观测波形与在弱阻尼蓄水层系中由阶梯状压力水头变化而引起的理论水井水位响应的解析表达式一致。由此一致性,我们可以从观测水文记录中估算出水井蓄水层系的参数和压力水头变化的位移分量。从最近台站的地震记录得出,在14次事件中仅有7次,包括很大位移的2次,明显与震群同时发生。这7次事件中最大的2次已被定量地解释为同震体应变变化的结果。其余5次解释为靠近体应变场节点的同震应变变化的影响,或其他同震的影响。同时,7次未与地震事件同步发生的水位变化也说明了在距井几十米距离内,蓄水层中突发了局部压力扰动。     

IRIS数据管理系统：它的发展,现状和计划方向

引言在过去的7年里,位于西雅图的IRIS数据管理中心的数据存档已成为地震学家为研究地球内部和震源情况而收集地震数据的数据源。在这些数据存档中,包含有执行IRIS PASSCAL项目期间部署的临时地震台站的数据,有IRIS全球地震台网的永久台站的数据,数字地震台网联盟的其他合作成员组织台网的数据以及来自美国地质调查局运行的早期数字台网的重要数据,由于中心还提供了获取这些波形数据有效方法,而成为世界上最大的地震波形数据的汇集中心。在大地震发生后的几小时内,地震学     

Attenuation characteristics of peak acceleration in North China and comparison with those in the eastern part of North America

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北岭地震20年后

城市地震,如1994年的6．7级北岭地震,为我们这些人清晰了解地震危险性的工作提供了的独特时刻。记得我是1994年1月17日清晨4点31分在我帕萨迪纳的家中被震醒的。当我匆忙地赶到加州理工学院校园内美国地质调查局（USGS）我的办公室时,我记得想知道的是那天会带来什么。震中区人烟稀少呢？还是我们只能接受直接击中了已经城市化的洛杉矶？现在我们知道,虽然破坏性的震动延伸到了洛杉矶盆地,但真正受到剧烈震动的是圣费尔南多谷;5台强震加速度计记录的地震动峰值速度（PGV）超过了1m／s。     

Dispersion and toxicity to non-target aquatic organisms of pesticides used to treat sea lice on salmon in net pen enclosures

Pesticides are used extensively in the finfish aquaculture industry to control sea lice infestations on farmed salmon. The most prevalent method of use is to enclose a net pen with an impervious tarpaulin and mix a pesticide solution within that enclosure. After treatment for short periods (1 h) the pesticide solution is released to the environment. Concerns have been raised that there is a potential risk to non-target aquatic organisms from those releases. The fate of dispersing pesticide solutions was measured after six simulated treatments in the Lower Bay of Fundy, New Brunswick. Three simulated treatments were done with azamethiphos and three with cypermethrin. Rhodamine dye was added to all pesticide solutions in order to facilitate tracking of the dispersing plume through real-time measurements of dye concentrations by a flow-through fluorometer coupled with a differential global positioning system (DGPS). Water samples were obtained from within the plumes at various times after release and analysed for pesticide content and toxicity to a benthic amphipod Eohaustorius estuaris. Dye concentrations were detectable for time periods after release which varied from 2 to 5.5 h. Distances travelled by the dye patches ranged from 900 to 3000 m and the dye concentrations at the final sampling period were generally 1/200-1/3000 the pre-release concentrations and cypermethrin concentrations were generally 1/1000-1/2000 the pre-release concentrations. Cypermethrin concentrations in water samples were closely correlated with dye concentrations, indicating that dye analyses were an accurate surrogate for cypermethrin concentrations. Most samples taken after the releases of azamethiphos were not toxic to test organisms in 48 h exposures and none were beyond 20 min post-release. By contrast, almost all samples taken after the release of cypermethrin, even up to 5-h post-release, were toxic. Data indicate the potential to cause toxic effects over areas of hectares from a single release of cypermethrin.