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1D Seismic Velocity Model with GT5
Events in Brazil and Tests of Crustal
Thickness Corrections to Improve the
RSTT Model for South America
Marcelo Assumpção; Elder Marco; José Roberto Barbosa
Geophysics Dept.
University of São Paulo
Seismic Travel Time Models
T1-01 Thu 09:10
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Status report on the RSTT project
in Brazil
• GT5 and Pseudo-GT events in Brazil
• Travel time database
• Test of Crustal Corrections
• Proposed 1D reference model for Brazil
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Brazil Network: 70 stations installed by four institutions
Project funded by
USP –
São Paulo
Rio de Janeiro
Natal
UnB –
Brasília
LPAZ
SAML
PTGA
RCBR
CPUP
BDFB
SPB
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Feng et al., 2007; Assumpção et al., 2013
Lithospheric mantle in Brazil has higher than average velocity
~5% higher velocity,
on average.
But also, significant
lateral variation.
3D models are
needed to improve
locations.
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Travel time database
distance, km
T –
X/8
.5
IASP91 Herrin
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Example of GT5 event: hypocenter with local network (±
1km).
Chimpliganond et al., 2010
Itacarambi, MG, Mag=4,7
09-Dec-2007
USGS
NW SE
hypodd
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Pseudo GT: known hypocenter from aftershocks
Origin time estimated with teleseismic stations (IASP91)
Porto dos Gauchos,
MT, mag=5,0 23-Mar-2005
Barros et al., 2009
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Aseismic country – few GT events…none up to 2012; four available now at ISC
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Residuals for Herrin’s (1968) model.
Travel times corrected to 0 depth hypocenter.
distance, km
Re
s =
Ob
serv
-Mo
de
l (s
ec)
No Crustal correction
Residuals (s)
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Correcting for crustal thickness variation
Assumpção et al.(2013)
Travel times corrected
to 40 km depth, at
both epicenter and
station.
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Residuals for Herrin’s (1968) model.
Travel times corrected to 0 depth
distance, km
Re
s =
Ob
serv
-Mo
de
l (s
ec) No Crustal correction
Re
s =
Ob
serv
-Mo
de
l (s
ec)
Corrected to 40 km Crust
s
s
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Residuals for RSTT model(currently CRUST2.0 for S.America)
Re
s =
Ob
serv
-Mo
de
l (s
ec)
distance, km
residual, sec
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Best 1D model
for Brazil
(New BR):
Pc=6.1 km/s
H= 42 km
Pn= 8.1 km/s
gradient =
1.57 m/s/km
T –
X/8
.2GT5 pGT
distance, km
Herrin
BR
model
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Fast and Slow Paths for New BR Model
FAST SLOW
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Fast and Slow Paths
for New BR Model
S-wave anomaly at
100 km depth
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Conclusions - 1
Crustal correction is
relevant but reduces
scatter only slightly
No correction
Corrected
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Conclusions - 2
Preliminary RSTT (CRUST2.0)
is better than Herrin and
similar to new 1D BR model
residual, sec
1D Herrin, crustal corrected
3D
residual, sec
1D New
BR crustal-
corrected
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Conclusions - 3
-Mantle variation is
more important than
crustal correction,
- Next steps:
a) Insert new crustal
model into RSTT
b) If enough data,
do a tomography
inversion (?)
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Thank youVielen Dank!
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Annex
Fast, slow paths wrt New BR model P-wave anomaly at 150 km depth