A seismological study of shallow weak micro-earthquakes in the urban area of Hamburg city, Germany, and its possible relation to salt dissolution
A seismological study of shallow weak micro-earthquakes in the urban area of Hamburg city, Germany, and its possible relation to salt dissolution
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DOI：
10.1007/s11069-011-9716-9
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发表时间：
2011-01
期刊：
影响因子：
3.7
通讯作者：
T. Dahm;S. Heimann;W. Bialowons
中科院分区：
文献类型：
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作者：
T. Dahm;S. Heimann;W. Bialowons
2009年4月8日至9日，复活节前的濯足节星期四午夜过后不久，汉堡大弗洛特贝克的几个人感到异常强烈的地面震动，其中一些人因为害怕地震而离开了房屋。警察和消防队接到了忧心忡忡的居民的电话。几天后，人们在互联网上公布了他们的观察结果。2009年4月21日，当地时间晚上8时左右，第二次有震感。据我们所知，没有发生建筑物或基础设施受损的情况。汉堡大学地球物理研究所于2009年4月22日至5月17日在震中地区安装了三个临时地震台站。收集了附近两个台站（1公里处的Deutsches Elektronen-Synchrotron和7公里处的地球物理研究所）的地震数据，并将其纳入时间网络。这些事件发生在Othmarschen Langenfelde盐底辟的顶部上方，该地区以活跃的天坑形成和以前的历史性地面震动事件而闻名。地震学资料分析表明，4月8日至21日，在100 m左右的深度发生了3次浅源微震，最大的一次为Mw0.6左右。这种浅层事件的深度定位是困难的标准方法，并在这里受到表面波的波形建模。地震发生在最高100米的软沉积物中是一种罕见的现象，无法用标准模型解释。软沉积物中的破裂过程不同于较强岩石中断层上的破裂过程。我们讨论的背景下，以前的历史地震和现有的天坑和变形数据的事件的破裂和震源机制。虽然该事件很弱，但0.3 s的破裂持续时间却异常长。三种可能的模型产生的重复地面震动事件在格罗斯Flottbek的开发和讨论，意味着退出不同的危害沉降，地面运动，天坑形成。我们所支持的模型假设，屋顶破坏发生在震中下方约100米深的现有土腔中。其他地质灾害较小的模型无法用现有数据加以反驳，但可计划未来的地球物理实验来解决这个问题。
In the night from 8/9 April 2009, shortly after midnight on Maundy Thursday before Easter, several people in Gross Flottbek, Hamburg, felt unusual strong ground shocks so that some of them left their houses in fear of earthquake shaking. Police and fire brigade received phone calls of worried residents. A few days later, Internet pages were published where people reported their observations. On 21 April 2009 at about 8 p.m. local time, a second ground-shaking event was felt. Damage to buildings or infrastructure did not occur to our knowledge. The Institute of Geophysics, University of Hamburg, installed from 22 April to 17 May 2009 three temporal seismic stations in the epicentral area. Seismological data from two nearby stations at the Deutsches Elektronen-Synchrotron at 1 km and the Geophysical Institute at 7 km distance were collected and integrated to the temporal network. The events occurred above the roof of the shallow Othmarschen Langenfelde salt diapir, in an area known for active sinkhole formation and previous historic ground-shaking events. The analysis of the seismological data shows that three shallow micro-earthquakes occurred from 8 to 21 April at a depth of about 100 m, the largest one with a moment magnitude of aboutMW0.6. Depth location of such shallow events is difficult with standard methods and is here constrained by waveform modeling of surface waves. Earthquakes occurring in soft sediments within the uppermost 100 m are a rare phenomena and cannot be explained by standard models. Rupture process in soft sediments differs from those on faults in more competent rock. We discuss the rupture and source mechanism of the events in the context of previous historic shocks and existing sinkhole and deformation data. Although the event was weak, the rupture duration of 0.3 s was unusual long. Three possible models for the generation of repeated ground-shaking events in Gross Flottbek are developed and discussed, implying quit different hazards for subsidence, ground motion, and sinkhole formation. Our favored model postulates that roof failure occurs in an existing soil cavity beneath the epicenter at a depth of about 100 m. Other models bearing a smaller geo-hazard cannot be disproved with the data available, but future geophysical experiments may be planned to resolve this question.