عنوان مقاله [English]
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, and previously no clear relationship between tidal forces and seismic events with strike-slip faults has been seen.
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 onwards have been used.
Out of a total of 188 seismic events with a magnitude of more than 2 around the fault, after removing the foreshocks and aftershocks by the Reasenberg method and considering the completed magnitude (Mc = 2.8), 84 events were studied.
With consideration of superficial fault information and the internal position of the earthquakes, 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 parts, 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.
According to the model of fault parts, the main tidal stress components (two horizontal components and one vertical component) and shear stress are framed into the modeled plate. Events are examined in the frame of modeled plates by Schuster test and binomial method, in two conventional modes of 360 and ±180 degrees fuzzy.
Impact Outcomes These results are a bit complex. However, the results of the Schuster 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), could not assume a relation between earthquakes and tidal forces, but some are also classified, confirming this relation at specific intervals for different tidal components. For example, the components of tidal shear stress framed in the fault plate planes (parallel to the rupture of the fault main plane) are associated with a magnitudes range of 3-3.9. The binomial test also does not rule out seismic events in some fuzzy cases, where we expect the greatest effect of tidal stress on the dynamic sections of the fuzzy.
The Study of tidal components shows us that the negative values of the North-South horizontal component (direct to the 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 displace to the left and facilitates fault plane rupture and can cause earthquake triggering.
Keywords: tidal stress, Schuster test, Mosha strike-slip fault, the mathematical model of the fault.