Abstract
Seismotectonic deformations in the Middle America Trench and their features in the area of preparation of the Chiapas earthquake, М W =8.2, 08 September 2017, were determined using the data on 2244 focal mechanisms of earthquakes for the period of 1977–2017. The distribution of seismicity with depth was studied in detail. The decrease in the depth of the Benioff zone in the north-western subduction segments and the increase in the south-eastern segments is associated with the age of the subducting parts of the Cocos plate and the angle of their immersion. The latter mechanism can also explain the presence of earthquakes with normal focal mechanism on the oceanic uplift in the south-eastern segments of the subduction zone and their absence in the north-western ones. In general, the typical character of subduction deformations has a number of features in the Middle America Trench. The predominance of shortening by horizontal components and elongation by vertical ones at depths up to 35 km is replaced by the transitional type with mosaic distribution of deformations of different signs in the depth range of 36–70 km. Even lower, in the depth range of 70–105 km, the type of deformation changes to the opposite with respect to the upper horizon. The Chiapas earthquake occurred on the border of regions with different types of deformation, which indicates softening of the block’s medium to the west of the hypocenter and its hardening to the east. Such a state of the lithospheric medium may indicate the presence of a deformation shadow zone in the Chiapas earthquake preparation area.
Highlights
Seismotectonic deformations in the Middle America Trench and their features in the area of preparation of the Chiapas earthquake, МW=8.2, 08 September 2017, were determined using the data on 2244 focal mechanisms of earthquakes for the period of 1977–2017
The decrease in the depth of the Benioff zone in the north-western subduction segments and the increase in the south-eastern segments is associated with the age of the subducting parts of the Cocos plate and the angle of their immersion
The latter mechanism can explain the presence of earthquakes with normal focal mechanism on the oceanic uplift in the south-eastern segments of the subduction zone and their absence in the north-western ones
Summary
Первое из них – землетрясение Чьяпас 8 сентября 2017 г. – землетрясение Чьяпас произошло в районе залива Теуантепек 8 сентября 2017 г., φ = 15.022°, λ = –93.899°, Мw = 8.2, Н = 47 км [USGS Earthquake Hazards Program, 2017];. В очаге сильнейшего землетрясения Чьяпас (8 сентября 2017 г.) сбросовая подвижка произошла по крутой плоскости [USGS Earthquake Hazards Program, 2017]. Представляет большой интерес рассмотрение особенностей характера деформирования среды на разных глубинах на участках зоны субдукции, где готовилось землетрясение Чьяпас и последовавшие за ним события. (до землетрясения Чьяпас) насчитывает более двух тысяч определений для всей Центрально-Американской зоны субдукции, включая границы плиты Кокос. Наиболее интересный для нас район подготовки землетрясения Чьяпас в этих работах приурочен, как правило, к границе участков исследований. Это определяет актуальность изучения сейсмотектонических деформаций в Центрально-Американской зоне субдукции в целом, что позволит, в том числе, изучить их особенности в области подготовки землетрясения.
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