Proceedings of the 31st Technical Session of Geological Society of Sri Lanka
Published Online - 27th February 2015 (http://www.gsslweb.org)
GSSL-2015-01
Is the Mohorovicic Seismic Discontinuity the Bed of Earthquakes?
Atula Senaratne
Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka.
e-mail: [email protected]
The Mohorovicic discontinuity, or “Moho”, is the boundary between the crust and
the mantle. It occurs at an average 8 km below the bottom of the oceans and
about 32 km beneath the continents. At this discontinuity, seismic waves tend to
accelerate as the material below this level seems to be of high density.
250
200
150
100
50
0
0
7
14
21
28
35
42
49
56
64
71
80
87
95
104
113
127
141
156
179
204
225
289
460
580
631
No. of Earthquakes
The Significant Earthquake Database of the National Geophysical Data Center of
NOAA (NGDC/WDS-2015) contains information on destructive earthquakes from
2150 B.C. to the present. Earthquakes occurred since the year 1900 to date having
a magnitude above 6.0 have been selected for the present study. Each event is
presented with the date, the epicenter with longitude and latitude, the depth to
loci and the magnitude. Statistical analyses of these data revealed that the loci of
145 earthquakes of a total of 1573 clusters at a depth of 10 km and 234 of 1573
found to occur at a depth of 33 km. This finding is in par with Mohorovicic’s (1909)
interpretation of seismic waves which led to establish “Moho” at 8 km below the
Depth in km
surface of oceanic crust and 33 km below the surface of the continents. High
seismic activity at the Moho discontinuity indicates the movements of the crust
over the mantle which is not clear in available literature. This paper proposes that
the “Moho” be the bed of earthquakes.
References: NGDC/WDS (2015) Significant Earthquake Database of the National Geophysical
Data Center of NOAA, USGS.
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