Overview ta3520Introduction to seismics

• Fourier Analysis• Basic principles of the Seismic Method• Interpretation of Raw Seismic Records• Seismic Instrumentation• Processing of Seismic Reflection Data• Vertical Seismic Profiles

Practical:• Processing practical (with MATLAB)

The seismic record

Body waves:

Surface waves:

A seismic shot record on land

Linear event:Direct/refraction

Linear event:Slower, Direct

Slightly hyperbolicevent: Reflection

Linear event:Very slow, Direct

Interpretation of seismic land record

thic

kn

ess 2

00

m

source detector

offset

air wave

surface wave(velocity 1850 m/s)

refraction

velocity 340 m/s

velocity 3500 m/s(P waves)

velocity 4800 m/s

Modelling of seismic land record

Observed data Modelled data

(ray theory approx.)

refraction

direct P-wave

surface wave

reflection

reflection

direct air wave

A seismic shot record at sea

Linear event:Refraction

Many Hyperbolic events: Reflections

Linear event: Direct

First hyperbolic event: primary reflection

Hyperbolic event at twice timeof primary reflection: multiple

Interpretation of marine record

30

0 msource detecto

r

offset

direct P wave

refraction velocity 240 m/s

velocity 1500 m/s(P waves)

velocity 1500 m/s(density different)

25

0 m

reflection

multip

le

reflection

Modelling of marine record

Observed data Modelled data

(ray theory approx.)

refractiondirect P-wave (water)

reflectionsmultiple reflectionmultiple reflection