omar

Geophysical Exploration using Seismic Refraction

to interpret geologic layers of the subsurface in

the southeastern part of the Espanola Basin,



SAGE 2001



Omar Abou-Ismail

University 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

T =0.24 s

3





V =4.3 km/s

3





T =0.13 s

2





V =1.84 km/s

2

ti v2v1

t v2v1 h1 

h1  i  21m

v 

1

2

v  v

1 2 2 2

2

v

2 2 2 2 1

2 1

h  t  22 v 21v   v v

 

1

2 2 2

 h 

2h1 v3  v1 v 2

1 3 1 3 1





h2  ti 2    23v 1  v  165m

2 i2

v 3 1



vv  2

1

2 2

 

  2 22

 

3 1

1

v3v1



  2 v3  v1



•Total Amount of Offset = 311m/4000,000y = .078 mm/yr

Average 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”