TITLE:
Deep and Ultra-Deep Earthquakes Worldwide, Possible Anomalies in South America
AUTHORS:
M. Hagen, A. Azevedo
KEYWORDS:
Deep Earthquakes (DQ), Ultra-Deep Earthquakes (UDQ), South America
JOURNAL NAME:
Natural Science,
Vol.10 No.6,
June
28,
2018
ABSTRACT: The aim of this paper is to evaluate the worldwide variation of deep and ultra-deep earthquakes
(DQ and UDQ) during the period 1996-2017. This project found only three locations
around the globe presenting this kind of seismicity. Although there are other global settings
showing deep seismicity, they are not periodical and cannot be considered by a statistical
view. The three areas with intense activity for DQ and UDQ events are located mostly in
subduction areas. The largest variations of DQ and UDQ border the Pacific Ocean and include
the North Pacific, South Pacific, and South America. The major difference in this set
is that the first two sites are subduction zones and the South American occurrences happened
in the interior of the continent. Another anomaly is an internal layer between 300 -
500 km in South America that shows no tremors in the period studied. However, below 500
km activity reappears, even at extreme depths of up to 650 km. We suggested that the reason
for those occurrences would be due to an anomaly in the asthenosphere in this region. This
anomaly would probably be presenting a breakable material that was pushed by the Nazca
platform against the South America plate. Other depths below 100 km in all the regions are
discussed as well. We suggested that the reason for those occurrences was an anomaly
created in the asthenosphere as part of the process of the South America collision with the
Nazca plate. Part of the Nazca plate has subducted below South America, creating a slab as
deep as 500 km. The convergent slab is still moving against South America and sinking due
to the gravity and rotation of the Earth. The discrepancies in the occurrences we tracked at
different locations indicated that this slab had different thicknesses around South America.
We found similar results for Vanuatu and Fiji; in these regions UDQ events occur at the
subduction zones under the ocean with depths greater than 700 km. Here, a possible explanation
is that part of the lithosphere is subducted at these depths and is causing tremors.