Seismic Sequence Structure and Earthquakes Triggering Patterns

Paolo Balocchi,Giulio Riga

doi:10.4236/ojer.2016.51003

Abstract

Within a time distribution of magnitude values, before any mainshock some earthquake triggering patterns with several features develop, under tectonic processes’ influence, through which it is possible to early identify the preparation phase of big earthquakes. The purpose of this article was to identify and classify the warning patterns that develop before a big earthquake by considering space-time seismicity variations. The methodological approach adopted was of graphical type, based on procedures of technical analysis currently used to estimate the financial markets. In the initial phase of the study we have analyzed the seismic sequences types described in the bibliography (type 1: foreshocks-mainshock-aftershocks, type 2: mainshock-aftershock; type 3: swarm) and the main structure of the seismic cycle, within which maximum and minimum magnitude values characterize the pattern that it develops until the main event changes. Then, we assessed the position of foreshocks, mainshock and aftershocks within the seismic cycle in order to identify the warning pattern that characterized the exact time when the energy emission occurs. As to the evolution normally shown over time, we have grouped the warning patterns in 2 categories: 1) progressive earthquake pattern; 2) flash earthquake pattern. Finally, we have made a classification of the warning pattern related to the fluctuations of maximum and minimum magnitude values, compared its form with the mainshock’s focal mechanism and suggested some graphic procedures in order to estimate the mainshock magnitude value associated with each warning pattern. The results we obtained unquestionably allow a better comprehension of preparation process of a large earthquake, improving the earthquakes forecasting probability in the next future.

Highlights

The checks we have performed on several big earthquakes occurred in the last 40 years, have highlighted that it is possible to identify some earthquakes triggering patterns in the short and medium term, whose space-time complexity is strictly linked to the following items: a) the seismic region heterogeneity [1]; b) the stress state inside and around the source of a big earthquake [2] [3]; c) the long-range interactions among different seismic and heterogenic regions
The identification, in advance, of the warning pattern within the seismic sequence, provides several useful insights to understand what is happening in the source region area, which can be used to improve earthquakes predictions
The methodological approach adopted for the classification of earthquake triggering patterns and the assessment of the main earthquake magnitude is based on the technical analysis [7] [8], which consists in a methodology for the evaluation of financial markets used to identify trends and assess future trends possibility

Summary

Introduction

The analysis of the seismic sequence structures underlines (points out) that magnitude values do not unpredictably change, but follow some trends that can be identified in a chart.Starting from this principle, we can speculate that some behaviors cyclically recur, making it possible, if identified on time, for the formulation of hypothesis about the future evolution of the seismic sequence.The checks we have performed on several big earthquakes occurred in the last 40 years, have highlighted that it is possible to identify some earthquakes triggering patterns in the short and medium term, whose space-time complexity is strictly linked to the following items: a) the seismic region heterogeneity [1]; b) the stress state inside and around the source of a big earthquake [2] [3]; c) the long-range interactions among different seismic and heterogenic regions.The identification, in advance, of the warning pattern within the seismic sequence, provides several useful insights to understand what is happening in the source region area, which can be used to improve earthquakes predictions.Below, we will explain the known seismic sequences features, which include warning patterns we have classified and discussed in relation to the magnitude values’ trend.We performed the analysis of the seismic sequence using: a) spatial coverage of datasets ranging from portions of a region to several countries (from a few tens of kilometers to thousands of kilometers); b) magnitude range of 2.0 - 10 M; c) depths range of 1 - 50 km. The analysis of the seismic sequence structures underlines (points out) that magnitude values do not unpredictably change, but follow some trends that can be identified in a chart. Starting from this principle, we can speculate that some behaviors cyclically recur, making it possible, if identified on time, for the formulation of hypothesis about the future evolution of the seismic sequence. We performed the analysis of the seismic sequence using: a) spatial coverage of datasets ranging from portions of a region to several countries (from a few tens of kilometers to thousands of kilometers); b) magnitude range of 2.0 - 10 M; c) depths range of 1 - 50 km

Objectives

Methods

Findings

Conclusion