Investigation of the relationship between tidal stress components and seismic events in the area of Mosha fault

Document Type : Research Article

Authors

1 Ph.D. Student, Ferdowsi University of Mashhad, Faculty of Science, International Pardis, Mashhad, Iran

2 Professor, Ferdowsi University of Mashhad, Faculty of Science, Director of Geology's Department, Mashhad, Iran

3 Associate Professor, Ferdowsi University of Mashhad, Faculty of Science, Department of Geology, Mashhad, Iran

4 Assistant Professor, Ferdowsi University of Mashhad, Faculty of Science, Department of Geology, Mashhad, Iran

Abstract

Studies show that celestial bodies can be effective in triggering earthquakes from several perspectives by exerting gravitational forces, albeit less than cumulative tectonic forces. These forces in the fluid environment increase the pore pressure and facilitate the rupture and seismicity of the earthquake. Previously, no clear relationship between tidal forces and seismic events with strike-slip faults has been reported.
    In this study, the relationship between earthquakes and tidal stress components in the fault area along the sinistral strike-slip of Mosha was investigated. For this purpose, IIEES and NEIC seismic data from 1975 to 2020 have been used.After removing the foreshocks and aftershocks by the Reasenberg method and considering the magnitude of completeness (Mc=2.8), 84 seismic events out of 188, with a magnitude of more than 2 around the fault were studied.
    By considering the superficial fault information and the hypocenter of the earthquakes and assuming that the events occurred on the fault plane, the mathematical equation of the fault plane is fitted and modeled.
According to the model of the presented fault segments, the main and shear stress components were included and calculated in the frame with the help of the conversion matrix. The results show that the north-south horizontal component of tidal stress has the greatest effect on tectonic forces and facilitates seismic shock. Based on the model of fault segments, the main tidal stress components (two horizontal components and one vertical component) and shear stress are framed into the modeled plane. Events are examined in the frame of modeled planes by Schuster’s test and binomial method, in two conventional modes of 360 and ±180 degrees of tidal phases.
    Outcomes of these results are a bit complex. However, the results of the Schuster’s test at the test level of 5% (significance level 95%) do not show the correlation between tidal forces and earthquakes in the general case (in magnitude range 2.8-4.9) and we could not assume a relation between earthquakes and tidal forces, but using the classified magnitudes confirms this relation at specific intervals for different tidal components. For example, the components of tidal shear stress framed in the fault plane (parallel to the rupture of the fault main plane) are associated with a magnitude range of
3-3.9. The binomial test also does not rule out seismic events in some phase cases, where we expect the greatest effect of tidal stress on the dynamic sections of the phase.
   The study of tidal components shows that the negative values of the north-south horizontal component (towards south) play an important role to decrease the minimum tectonic stress at the beginning of the rupture, which is northward and as a result, the Mohr envelope failure tends to shift to the left. It facilitates fault plane rupture and can cause earthquake triggering.

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References

Iranian Journal of Geophysics
Volume 17, Issue 1
March 2023
Pages 57-88

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