A novel technique for measuring Lg attenuation—results from Eastern Canada between 1 to 10 hz
A novel technique for measuring Lg attenuation—results from Eastern Canada between 1 to 10 hz
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发表时间：
1987-04
影响因子：
3
通讯作者：
K. Chun;G. West;R. Kokoski;C. Samson
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作者：
K. Chun;G. West;R. Kokoski;C. Samson
使用加拿大东部遥测台网台站和魁北克格伦阿尔蒙德（GAC）的补充地震研究观测站的垂直分量速度地震图，详细研究了区域记录的Lg波在0.6和10 Hz之间的频谱振幅。我们发现，这些站之间的站点响应不同的频率范围内的兴趣超过3的一个因素。此外，他们被发现是强烈的频率依赖性。因此，在研究区域地震记录的Lg波衰减和Lg源谱时，必须考虑它们。本文提出了一种与传统的两站法密切相关的测量站间面波衰减的新方法。在保留传统的两站法的所有可取的功能，新的技术，我们将称为“反向两站法”，允许简单，直接（一个参数）的Lg波衰减的测定稀疏的频谱数据的方式不受站址效应和相关的仪器误差。反向两站的方法是成功地测试弱衰减，短（53至210公里）站间的路径在加拿大东部，一个困难的实验条件下正常的标准。加拿大东部的Lg衰减系数（0.6至10 Hz）与频率有关，其形式为γ（f）= 0.0008 f 0.81 km−1。在较高频率下，Lg衰减似乎基本上与频率无关。后者的发现被初步解释为证据表明，区域记录的Lg波在加拿大地盾，如在Lg波传播通过结构复杂的阿巴拉契亚省的情况下，由Sn波的高频尾波污染。屏蔽路径上的Lg污染从14 Hz开始变得严重，14 Hz是在阿巴拉契亚省传播的Lg信号完全由非Lg到达主导的频率的两倍。
Spectral amplitudes of regionally recorded Lg waves are studied in detail between 0.6 and 10 Hz, using vertical-component, velocity seismograms of the Eastern Canada Telemetered Network stations and a supplementary Seismic Research Observatory-type station at Glen Almond (GAC), Quebec. We find that the site responses vary among these stations by more than a factor of 3 within the frequency range of interest. Furthermore, they are found to be strongly frequency dependent. Consequently, it is essential that they be taken into consideration in studies of Lg wave attenuation and Lg source spectra of regionally recorded seismic events. We present a new method of measuring interstation surface wave attenuation, which is closely related to the conventional two-station method. While retaining all the desirable features of the conventional two-station method, the new technique, which we will call the “reversed two-station method,” allows simple, direct (one-parameter) determination of the Lg wave attenuation from sparse spectral data in a manner unaffected by station site effects and associated instrument error. The reversed two-station method is successfully tested over weakly attenuating, short (53 to 210 km) interstation paths in eastern Canada, a difficult experimental condition by normal standards. The Lg attenuation coefficient (0.6 to 10 Hz) in eastern Canada is found to be frequency dependent and of the form γ( f ) = 0.0008 f 0.81 km−1. At higher frequencies, the Lg attenuation appears to be essentially frequency independent. This latter finding is preliminarily interpreted as evidence that regionally recorded Lg waves in the Canadian Shield are, as in the case of Lg waves propagating through the structurally complex Appalachian Province, contaminated by the high-frequency coda of Sn waves. The Lg contamination over the shield paths becomes severe starting at 14 Hz, twice the frequency above which the Lg signal propagating over the Appalachian Province becomes completely dominated by non- Lg arrivals.