Aftershocks Identification and Classification

Abstract

Usually, earthquakes develop after a strong main event. In literature they are defined as aftershocks and play a crucial role in the seismic sequence development: as a result, they should not be neglected. In this paper we analyzed several aftershock sequences triggered after a major earthquake, with the aimed at identifying, classifying and predicting the most energetic aftershocks. We developed some simple graphic and numeric methods that allowed us to analyze the development of the most energetic aftershock sequences and estimate their magnitude value. In particular, using a hierarchisation process related to the aftershocks sequence, we identified primary aftershocks of various orders triggered by the mainshock and secondary aftershocks of various orders triggered by the previous shock. Besides, by a graphic method, it was possible to estimate their magnitude. Through the study of the delay time and distance between the most energetic aftershocks and the mainshock, we found that the aftershocks occur within twenty-four hours after the mainshock and their distance remains within a range of hundreds of kilometers. To define the aftershocks sequence decay rate, we developed a sequence strength indicator (ISF), which uses the magnitude value and the daily number of seismic events. Moreover, in order to obtain additional information on the developmental state of the aftershocks sequence and on the magnitude values that may occur in the future, we used the Fibonacci levels. The analyses conducted on different aftershocks sequences, resulting from strong earthquakes occurred in various areas of the world over the last forty years, confirm the validity of our approach that can be useful for a short-medium term evaluation of the aftershocks sequence as well as for a proper assessment of their magnitude value.

Temporal properties of aftershock sequences of large earthquakes in Iran - Analysis of primary and secondary aftershocks of the Ezgeleh sequence

“…However, we found no systematic pattern of changes for the parameter. The branch structure method [Riga and Balocchi, 2017] on the Ezgeleh earthquake sequence could successfully estimate the occurrence of an event with magnitude about 6.4, which its evidence was the occurrence of the earthquake = 6.4 on 25/11/2018.…”

“…Also the seismicity map of the region is presented in Figure 7. The type of aftershocks of the Ezgeleh earthquake is analyzed through the graphical method introduced by Riga and Balocchi [2017] and the primary and secondary aftershocks were distinguished. Figure 8 presents the branch structure for the Ezgeleh earthquake during 15 months; starting from three months before the occurrence of the main event to 12 months after that.…”

“…Of course, in some cases, seismic waves caused by the main event can lead to change the stress of the fluids into adjacent fault holes, which reduces the strength (static friction) on the adjacent faults and creates aftershocks [Shcherbakov et al, 2005]. Also, as stated by Riga and Balocchi [2017] the aftershocks are classified by Kisslinger [1996] into three sets: aftershocks occurring in the rupture area of the main fault plane, aftershocks occurring in the main fault plate, but outside the rupture area and aftershocks outside the main fault.…”

“…Figure8. The branch structure of the Ezgeleh earthquake, the colored lines indicate the developmental stages, the pink stars indicated with letter F can be considered as foreshocks for M N = 6.4, according toRiga and Balocchi (2017).…”

Analysis of Aftershock Earthquake Decay in Mamberamo on September 10, 2022 using GEOSTAT V2.0 Software

“…Aftershock is a series of earthquakes that occurred after the Mainshock. Generally, this series of earthquakes is smaller than the Mainshock and can last for days, weeks or even months [8] On September 10, 2022, there was an earthquake with a magnitude of M6.2 which triggered a series of aftershocks. Monitoring results from the Center for Meteorology Climatology Geophysics Region V (BBMKG V) noted that 93 aftershocks had occurred since one week after the main earthquake.…”