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