美国西部地区加卸载响应比的时空演化及地震活动性分析

摘要/Abstract

摘要： 美国西部地区位于环太平洋地震带, 该地震带是地球上地震活动最为强烈的地带, 为了研究该地区的地震活动性, 对该地区进行了加卸载响应比的时空扫描, 考察了该地区加卸载响应比异常区域的时空演化; 并用2001—2006年的扫描结果与次年实际发生的5级以上地震进行对比, 发现绝大部分的强震都发生在前一年的预测区域内。根据加卸载响应比的时空演化和该地区的最新扫描结果, 对未来地震活动性进行了分析。

关键词: 加卸载响应比(LURR), 时空扫描, 地震活动性, 美国西部地区

Abstract: The seismogenic process of a major earthquake is rather complicated. From the viewpoint of mechanics or physics, the essence of an earthquake is the damage, instability or failure of the focal media accompanied by a rapid release of energy. A new parameter-Load/Unload Response Ratio (LURR) has been proposed as a measure of this process. Using LURR as a precursor in earthquake prediction, retrospective examination of over hundred earthquake cases has been carried out, and more than 80% of the examined ones are well in agreement with that the peak of LURR, which appeared before the main shock and the peak value is much higher than 1. By the way, in the latest 4 years (2003—2006), the earthquake prediction with LURR method is satisfied, which was conducted in Chinese mainland at the end of every year.
The western United States lies on the Circum-Pacific zone, the most active seismic zone in the globe. In order to study the seismicity in western America, the spatial scanning of Load/Unload Response Ration in western America (30~50°N, 100~125°W) has been conducted and the evolution of the LURR anomalous region has been investigated. The comparisons of the LURR anomalous regions in 2001—2006 with the actual M≥5.0 earthquakes are performed respectively, which shows that 18 earthquakes with M≥5.0 occurred in LURR anomalous regions while 19 earthquakes with M≥5.0 in LURR regions in total when the scanning radius R=100 km and 20 earthquakes in LURR anomalous regions while 21 earthquakes in LURR regions when R=200 km. The statistical results show that LURR is a good precursor in earthquake prediction.
In order to analyze the seismicity in western America, the evolvement of the anomalous LURR regions is investigated. According to the evolution (figure 3 in the paper), some analyses have been carried out as below:
(1) In the rectangle zone of 45°N~49°N, 120°W~124°W, anomaly appears in Figure 3a, and keeps increasing, stays in high value during (g) to (m), decreases from (o) to (p), while there is no earthquakes with magnitude M5 or larger occurred during 2002 to 2007, so strong earthquakes (about M6) will probably occur in this region, and the magnitude and the probable occurrence time of earthquakes can be determined according to the formula Eq.3 in the paper.
(2) In the rectangle zone of 31°N~36°N, 115°W~118°W, in Fig.3, the anomalous LURR value rises from (a) to (b), and decreases at (c), at this time the No.17 earthquake (Sep. 2005) occurred in table 2; from (d) to (f) this region stays in rather high value, and rises at (g) and then the No.18, No.19 earthquakes occurred successively; the LURR value in this region keeps increasing from (h) to (j), and stay high value from (k) to (m) without any change, but the highest LURR point of this region has moved to south slightly; it decreases form (n) to (p), so the magnitude and time of the probable earthquakes also can be determined according to the formula of T₂ and M in the paper.
(3) In region around point 46°N, 110°W, from (a) to (b) the anomalous area gets bigger and value rises gradually, and then No.16 earthquake (Aug. 2005) took place. Although the scanning result in late 2004 (d) didn't appear any anomaly, some big anomalous areas with rising LURR value appeared from Mar. 2007 to Jun. 2007, indicating if we investigated the evolution of the LURR anomalous region, the No.16 earthquake could be predicted accurately. The anomalous region around this point appears again at (i) and the anomalous area gets bigger gradually, and the value rises during (m) to (p), we will keep an eye on this region and more scanning will be carried out, if the peak value of this region is appears, the magnitude and time of the probable earthquakes will be determined in terms of Eq.3.
(4) In region around point 40°N, 124°W, some small anomalous region appears in (a)~(b), and the area gets bigger in (c)~(h), and then No.20 earthquake occurred (Jul. 2006); the anomalous region keeps same in (i)~(m) and then No.21 earthquake occurred (Feb. 2007); the anomalous region gets smaller and disappears at last in (n)~(p), in this process No.23 earthquake (Jun. 2007) occurred in south of this region with short distance. So we think during the LURR anomalous process in this region, 4 earthquakes with magnitude M5 or lager occurred successively, in other words this region release energy successively during the anomalous process and will keep in a more peaceful state in the future 1 or 2 years.

Key words: Load/Unload Response Ratio (LURR), Tempo-spatial scanning, Western America, Seismicity

中图分类号:

P315.7

张浪平, 尹祥础, 梁乃刚. 美国西部地区加卸载响应比的时空演化及地震活动性分析[J]. 地震, 2008, 28(4): 29-38.

ZHANG Lang-ping, YIN Xiang-chu, LIANG Nai-gang. Study on the Tempo-spatial Evolution of LURR and Seismicity in Western America[J]. EARTHQUAKE, 2008, 28(4): 29-38.

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