Influence of tidal effects on the periodicity of earthquake activity in diverse geological settings with particular emphasis on submarine hydrothermal systems
Gp. Glasby et J. Kasahara, Influence of tidal effects on the periodicity of earthquake activity in diverse geological settings with particular emphasis on submarine hydrothermal systems, EARTH SCI R, 52(4), 2001, pp. 261-297
Hydrothermal earthquakes may be defined as earthquakes caused by the: hydro
fracturing of the oceanic crust by submarine hydrothermal fluids. It is sug
gested that they correspond to the cracking of the ocean crust at the britt
le-ductile transition that marks the downward limit of seawater circulation
into the ocean crust. Semi-diurnal variations in submarine hydrothermal di
scharge in backarc settings and at the crests of mid-ocean ridges have been
detected by hydrophone but no influence of tidal effects on the periodicit
y of microearthquakes around submarine hydrothermal vents has been observed
so far. Although tidal stresses are too small to initiate earthquakes them
selves. they may trigger earthquake activity when imposed on slowly increas
ing tectonic stress. These effects therefore tend to be observed in geologi
cally active regions where stress levels in the earth's crust are high. The
influence of tides on the periodicity of microearthquakes tends to be comp
lex because the effects of ocean and earth tides are not uniform at the sur
face of the earth and because the microearthquakes occur in a wide variety
of geological settings. Earth tides cause compression and dilatation of the
oceanic crust which may be the most significant factor in initiating chang
es in fluid flow rate and microseismicity in submarine hydrothermal systems
. Much of the information now available on the tidal periodicity of microea
rthquakes is based on relatively short-term monitoring which lacks statisti
cal validity. The development and installation of deep-sea monitoring stati
ons will permit rigorous long-term monitoring programmes to be carried out,
which will lead to a better understanding of the nature and periodicity of
microearthquakes around submarine hydrothermal vents. (C) 2001 Published b
y Elsevier science B.V.