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| Titel |
Tendency of the Earth Oblateness change due to Earthquakes |
| VerfasserIn |
C.-L. Lo, B. F. Chao |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250023022
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| Zusammenfassung |
| The cumulative effect of earthquakes slightly and secularly decreases the Earth’s oblateness
parameter J2, making the Earth less oblate (rounder) (although “buried” in the much larger
decrease due to post-glacial rebound). Here we calculate the earthquake-induced,
cumulative-to-date change in J2 as a function of the radius in the Earth interior, ΔJ2 (r), of
all earthquakes according to the Global CMT catalog (close to 30,000 events from 1976). The
calculation is via the normal-mode summation scheme using the CMT moment tensor
for the seismic source mechanism on the SNREI Earth model PREM. The result
for earthquake-induced co-seismic ΔJ2 shows an average decreasing rate, -7.7
×10-13 per year, where ΔJ2 (r) also shows a decrease through the mantle and
core (including the core-mantle boundary), except near the crustal depth where
most earthquakes happen , and the ΔJ2 contribution from the mantle doubles that
from the core with time. We then attribute ΔJ2 to major earthquake types: normal
faulting and thrust faulting, and epicenter pole-ward or equator-ward to the nodal
latitude of the degree-2 order-0 Legendre function: 35.26˚ N or S. We find that
the secular tendency is decreasing ΔJ2 by thrust faulting and increasing ΔJ2 by
normal faulting, and decreasing ΔJ2 equator-ward to 35.26˚ and increasing ΔJ2
pole-ward to 35.26˚ . Among these conditions, the strongest tendency (decreasing)
is dominated by thrust faulting equator-ward to 35.26˚ N or S. We discuss and
speculate on the dynamics of this tendency in relation to Earth’s secular spin down. |
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