Geophysical Exploration using Seismic Refraction to interpret geologic layers of the subsurface in the southeastern

part of the Espanola Basin,

 SAGE 2001 

Omar Abou-IsmailUniversity of Utah

Picture Taken By Janet Yun Many Thanks…

Geology of the Espanola Basin• The Rio Grande Rift is a chain of

interconnected asymmetric basins extended from central Colorado to Chihuahua Mexico.

• The Espanola Basin is part of the Rio Grande Rift, established 3-5 million years ago in northern New Mexico, consists of sedimentary and volcanic rocks of Eocene to Quaternary age (Manley). Major rifting occurred in the Espanola Basin during the late Cenozoic causing the thinning of the upper crust. The eastern part of the basin consists partly of the Precambrian southern rockies; Sangre de Cristos Mountains. The western half consists of Jemez volcanic rocks. The La Bajada fault trends to the northwest with a displacement down to the southwest, separates the basin from the Santo Domingo subbasin to the south.

                 

This year geophysical work was done in the Santa Fe Embayment portion of the Espanola Basin and the north eastern part of the Albuquerque basin (Santo Domingo basin).

• Seismic Refraction– The length of the Seismic line is 3km. – The receivers are 25m apart. Each array had 6

geophones between the flag.

Note: Refraction surveys usually see 1/3 in depth of the length of the line. – “Sweeps” are created by the Vibroseis Truck and

data is collected. • Sweeps vibrate at a frequency of 8-80hz and lasts

approximately 8 seconds.

Location Map

Data Collected 1. Pick traveltime using recplt designed by Dr. John

Ferguson.

• Before Record is picked we have to adjust the trace gains to make the arrivals clearly visible.Gains are specified in decibels (dB).6 dB is a factor of 2 in amplitude. So 6 or 12 dB is approximately what we picked in order to check for correct level.

2. Travel time picks are then plotted by Tadplt.

Travel-time curves for basin (short offset)

Travel time curves for long offsets

3. Vision of models using modedt

Shallow basin

Deep refractors

Interpretation of Basalt Layer

T3=0.24 s V3=4.3 km/s

T2=0.13 s V2=1.84 km/s

( )m

vv

vvth i 21

22

12

12

2

121 =

−= ( )212

12

2

121 2

vv

vvth i

−=

( )( )

mvv

vv

vv

vvhth i 165

2

2

2

12

12

3

13

13

2

12

12

3122 =

−⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡−

−=( )

( )2121

23

13

13

2

12

12

3122

2

2

vv

vv

vv

vvhth i

−⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡−

−=

•Total Amount of Offset = 311m/4000,000y = .078 mm/yrAverage elevation across spread C is 1683 m, and the top of the basalt cap of the mesa is 1829 m, subtract the elevations and add the depth of the Basalt.

311 m Basalt Layer

165 m

The End

Many thanks to all the Seismic Refraction Team, “Over”