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布设在挪威的小孔径台阵NORESS是为改进高频段(1～15Hz)信噪比而设计的。虽然它的主要目的是增强检测和特征化区域距离上的弱地震事件的能力,但还发现这种台阵对于研究远震事件也是非常有效的,尤其是用在欧亚大陆。这主要有两方面的原因:(1)由于高Q值路径,欧亚地震和爆炸记录一般有较高的主频,通常在1.5～4.0Hz范围内,而该区域的噪声水平较低;(2)在此频率范围内,台阵有特别高的信噪比增益12～14dB(0.6～0.7m_b单位)。 NORESS台阵在线检测效能的分析表明,即使在小震中区内也有大的区域变化。这主要是源区底下的信号集中效应,类似于以前横跨大台阵观测的接收器集中效应。对NORESS记录的塞米巴拉金斯克试验场地下核爆炸的详细研究表明,相对于全球m_b,NORESS有明显的正m_b偏差。其在东部(沙甘河)最高(1.0m_b单位),而在西部(德格连/科尼斯坦)稍低(0.4m_b单位),尽管各区城内相当分散。分析NORESS台阵接收的一组塞米巴拉金斯克低当量核爆炸资料的观测信噪比,参考公开发表的俄文文献中给出的当量,我们估计,在正常的噪声条件下,NORESS台阵能检测到低到0.1kt全偶合的爆炸信号。但由于只有少量的参考事件且其中大量是推断的,给出一个精确的阈值是困难的。需要强调的是,在噪声水平异常高(如在大地震的尾波中)或偶合条件不是很佳(如在完全或部分空解偶)的情况下,这个检测水平是达不到的。还必须注意,事件识别阈值必须高于信号检测阈值。
The small aperture array NORESS, which is based in Norway, is designed to improve the signal-to-noise ratio in the high frequency range (1-15 Hz). Although its primary purpose is to enhance the ability to detect and characterize weak-earthquakes over regional distances, it has also been found that such arrays are also very effective for studying teleseismic events, especially in Eurasia. There are two main reasons for this: (1) Due to the high-Q path, the Eurasian earthquake and explosion records generally have higher dominant frequencies, usually in the range of 1.5-4.0 Hz, while the noise level in the area is relatively low. 2) In this frequency range, the array has a particularly high SNR gain of 12 ~ 14dB (0.6 ~ 0.7m_b units). An analysis of the on-line detection performance of the NORESS array shows that there is a large area change even in the mid-earthquakes. This is mainly the signal concentration effect under the source region, similar to the receiver concentration effect previously observed across large array. A detailed study of NORESS recorded nuclear explosions at the Semipalatinsk test site shows that NORESS has a significant positive m_b offset relative to global m_b. It is highest (1.0m_b units) in the east (Shagam) and slightly lower (0.4m_b units) in the west (Degene / Konstanz), although the districts are fairly decentralized. Analyzing the observed signal-to-noise ratio of a group of Semipalatinsk low-equivalent nuclear explosions received by the NORESS array, with reference to the equivalent given in the published Russian literature, we estimate that under normal noise conditions, the NORESS station Array can detect as low as 0.1kt full coupling of the explosion signal. However, given a small number of reference events and a large number of them being extrapolated, it is difficult to give a precise threshold. It should be emphasized that this level of detection is unattainable when the noise level is abnormally high (as in the coda of a major earthquake) or the coupling conditions are not very good (as in the case of full or partial null coupling). It must also be noted that the event recognition threshold must be above the signal detection threshold.