Seismic Travel Time Models T1-01 Thu 09:10 1D Seismic Velocity Model - - PowerPoint PPT Presentation

▶

Sep 05, 2022 45 likes •248 views

Seismic Travel Time Models T1-01 Thu 09:10 1D Seismic Velocity Model with GT5 Events in Brazil and Tests of Crustal Thickness Corrections to Improve the RSTT Model for South America Marcelo Assumpo; Elder Marco; Jos Roberto Barbosa

SLIDE 1

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

SLIDE 2

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

SLIDE 3

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

SLIDE 4

Feng et al., 2007; Assumpção et al., 2013

Lithospheric mantle in Brazil has higher than average velocity ~5% higher velocity,

n average.

But also, significant lateral variation. 3D models are needed to improve locations.

SLIDE 5

Travel time database

distance, km

T – X/8.5

IASP91 Herrin

SLIDE 6

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

SLIDE 7

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

SLIDE 8

Aseismic country – few GT events…

none up to 2012; four available now at ISC

SLIDE 9

Residuals for Herrin’s (1968) model. Travel times corrected to 0 depth hypocenter.

distance, km Res = Observ-Model (sec)

No Crustal correction Residuals (s)

SLIDE 10

Correcting for crustal thickness variation

Assumpção et al.(2013)

Travel times corrected to 40 km depth, at both epicenter and station.

SLIDE 11

Residuals for Herrin’s (1968) model. Travel times corrected to 0 depth

distance, km Res = Observ-Model (sec)

No Crustal correction

Res = Observ-Model (sec)

Corrected to 40 km Crust

s s

SLIDE 12

Residuals for RSTT model

(currently CRUST2.0 for S.America)

Res = Observ-Model (sec) distance, km

residual, sec

SLIDE 13

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/8.2

GT5 pGT

distance, km Herrin BR model

SLIDE 14

Fast and Slow Paths for New BR Model

FAST SLOW

SLIDE 15

Fast and Slow Paths for New BR Model S-wave anomaly at 100 km depth

SLIDE 16

Conclusions - 1

Crustal correction is relevant but reduces scatter only slightly

No correction Corrected

SLIDE 17

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

SLIDE 18

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 (?)

SLIDE 19

Thank you Vielen Dank!

SLIDE 20

Annex

Fast, slow paths wrt New BR model P-wave anomaly at 150 km depth