Download • earthquake locations define plate boundaries. • subduction of

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earthquake locations define plate boundaries.
subduction of oceanic plates underneath continental ones are causing most of the
earthquakes
earthquakes taking place below, on the already subducted oceanic plate, are showing up as a
thicker band of point distribution in these subduction zones.
diverging boundaries => not so many earthquake
subduction of Indian plate below Eurasian one (continent-continet convergent boundary) is
giving rise to a more widely spread out distribution of earthquakes. (why?)
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stronger earthquakes are mostly caused by oceanic-continental subduction (compression)
midoceanic ridges and intraplate earthquakes are mostly weaker
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deeper earthquakes are in the subduction boundaries (continent - oceanic)
earthquakes occour in the subducted part of the oceanic lithosphere, and moves deeper as
the subducted oceanic plates sink downwards
locations of earthquake sources in these regions reveal the geometry of the already
subducted plate
Indian plate subducting under Eurasian plate is not sinking much (as indicated by shallow
earthquakes and widely spread out distribution around 25-40N and 70-100E).
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subsurface earthquake depths around 20-23S and 180E (a roughly north-south subduction
boundary) indicating gemetry of the subducted plate moving right to left
the plate is subducting at an angle about 45deg and remaining solid and prone to failure up
to 700km depth
most of the earth quakes are shallow or are around 600km deep
Plot of freq distribution of earthquakes with depth (frequencies corresponding to depth more than
70 km are exagerrated by a factor of 5 for clarity).
the distribution is peaked near the surface and around a depth of 600km. (WHY?)
Instead of plotting total number of quakes, if the total energy realased is plotted similar curve is
obtained.
Plot of total number of quakes for a given values of exp(m), which is a measure of energy. The
probability of an earthquake of a given magnitude decreases with increasing magnitude values.
(what is this functional form?)