ReMi Applied Geophysics Spring Break 2010

ReMi Applied GeophysicsSpring Break 2010

Fariha IslamGretchen Schmauder

Question

• Can the ReMi method be used to locate faults in the Reno Basin?

Area Geology

• NE trending faults• Lacustrine, fluvial, and alluvial fan

deposits• Tertiary volcanic basement• Active hot springs

Abbott and Louie (2000)

Project Constraints

• Sedimentary cover can be greater than 1000 meters thick (Abbott and Louie, 2000).

• ReMi method typically used to depths less than 100 meters.

ReMi Method

• Surface wave velocity spectral analysis used to determine shallow earth structures

– Typically used to determine IBC site classification, rippability, void detection, and fault mapping.

ReMi Method

Fundamental Mode Rayleigh Wave

Transect 3 along lakeside dr.

ReMi Survey

Transect 4 along lakeside dr.

Survey location

Scott et al. (2004)

20 Transects along Manzanita Ln and adjacent streets

First order: shear velocity correlates to surficial geology

Tr ansect 14 Vs30 Model

-200

-150

-100

-50

00 500 1000 1500

Shear Wave Vel ocity (m/ s)

Depth

(m

)

Vs30 = 827 m/ s

NEHRP C l ass B

Tr ansect 2 Vs Model

-200

-150

-100

-50

00 100 200 300 400 500

Shear Wave Vel ocity (m/ s)

Depth

(m

)

Vs30 = 301 m/ s

NEHRP C l ass D

Tr ansect 5 Vs Model

-200

-150

-100

-50

00 500 1000

Shear Wave Vel ocity (m/ s)

Depth

(m

)

Vs30 = 407 m/ s

NEHRP C l ass C

Frary (2009)

Abbott and Louie (2000)

Second order: shear velocity correlates to depth to bedrock

Third order: correlation between shear velocity and faults?

Conclusions

• Transect velocity models reflect regional geology and depth to bedrock

• Correlation between velocity models and faults is inconclusive

• Indication that the alluvium has a lower shear velocity due to faulting

Further Work

• Additional ReMi lines south of Manzanita Lane to verify higher velocity in alluvium

• Better constraint on area faulting

references