*Earth Planets Space,* Vol. 63 (No. 3), pp. 315-324, 2011

doi:10.5047/eps.2010.12.007

## A new algorithm for the detection of seismic quiescence: introduction of the RTM algorithm, a modified RTL algorithm

Toshiyasu Nagao^{1}, Akihiro Takeuchi^{1}, and Kenji Nakamura^{2}

^{1}Earthquake Prediction Research Center, Institute of Oceanic Research and Development, Tokai University, Shizuoka, Japan

^{2}Graduate School of Marine Science and Technology, Tokai University, Shizuoka, Japan

(Received July 8, 2010; Revised December 16, 2010; Accepted December 19, 2010; Online published March 4, 2011)

**Abstract: **
There are a number of reports on seismic quiescence phenomena before large earthquakes. The RTL algorithm is a weighted coefficient statistical method that takes into account the magnitude, occurrence time, and place of earthquake when seismicity pattern changes before large earthquakes are being investigated. However, we consider the original RTL algorithm to be overweighted on distance. In this paper, we introduce a modified RTL algorithm, called the RTM algorithm, and apply it to three large earthquakes in Japan, namely, the Hyogo-ken Nanbu earthquake in 1995 (*M*_{JMA} 7.3), the Noto Hanto earthquake in 2007 (*M*_{JMA} 6.9), and the Iwate-Miyagi Nairiku earthquake in 2008 (*M*_{JMA} 7.2), as test cases. Because this algorithm uses several parameters to characterize the weighted coefficients, multiparameter sets have to be prepared for the tests. The results show that the RTM algorithm is more sensitive than the RTL algorithm to seismic quiescence phenomena. This paper represents the first step in a series of future analyses of seismic quiescence phenomena using the RTM algorithm. At this moment, whole surveyed parameters are empirically selected for use in the method. We have to consider the physical meaning of the "best fit" parameter, such as the relation of ΔCFS, among others, in future analyses.

**Key words: **
Seismicity, seismic quiescence, RTM, RTL, precursor.

Corresponding author E-mail: nagao@scc.u-tokai.ac.jp

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