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
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
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
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.
Travel time database
distance, km
T –
X/8
.5
IASP91 Herrin
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
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
Aseismic country – few GT events…none up to 2012; four available now at ISC
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)
Correcting for crustal thickness variation
Assumpção et al.(2013)
Travel times corrected
to 40 km depth, at
both epicenter and
station.
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
Residuals for RSTT model(currently CRUST2.0 for S.America)
Re
s =
Ob
serv
-Mo
de
l (s
ec)
distance, km
residual, sec
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
Fast and Slow Paths for New BR Model
FAST SLOW
Fast and Slow Paths
for New BR Model
S-wave anomaly at
100 km depth
Conclusions - 1
Crustal correction is
relevant but reduces
scatter only slightly
No correction
Corrected
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
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 (?)
Thank youVielen Dank!
Annex
Fast, slow paths wrt New BR model P-wave anomaly at 150 km depth