Transcript The Role of Active-Source Seismology in Earthscope

The Role of Active-Source
Seismology in EarthScope
Gary Fuis
U.S. Geological Survey
MAJOR LITHOS PHERIC DISCO VERIES
& CHIEF GEOPHYSICAL DISCOV ERY TO OLS
Fuis ’s lis t
DISCOVERY OF:
1.
2.
3.
4.
5.
Moh o
Be n io f f z o n e s
Sea flo o r s p rea d in g
Hot sp o t s
Thin- s ki nn e d te c t o n ic s in
oro g e n s ( e .g . , App al ac hian s )
6 . Pre c am b ria n subd u c ti o n
7 . Cru s t a l- sc ale w edg in g in
oro g e n s
8 . Sei s m ic b rig ht sp o t s in the
c ru s t
9 . Cru s t- pe n e tr a t in g f a ult s
1 0 . Pla t e - like a n o m a lie s in the
m a n t le
BY
ea rth q u ake s eism ology
ea rth q u ake s eism ology
(p ale o )m agn e tic- field map ping
ea rth q u ake s eism ology
re fle c tion pr o filing
re fle c tion pr o filing
re fle c tion pr o filing
ea rth q u ake s eism ology and ref le c tion
pr o filing
re fle c tion pr o filing
ea rth q u ake s eism ology
Trans-Canada Crustal
Cross-Section
Trans-Canada Crustal
Cross-Section
Trans-Canada Crustal
Cross-Section
Trans-Canada Crustal
Cross-Section
50 km
Cook et al., 2001
Flat Moho beneath crustal ramp Monashee Complex
Central Southern Cordillera
COCORP
Trans-Canada Crustal
Cross-Section
Active-Source Seismic
Methods
Active-source seismology falls
into 2 broad, overlapping
categories:
• Refraction seismology
• --gives a fuzzy image of structure but
provides constraints on rock
composition
• Reflection seismology
• --gives a detailed image of structure but
provides little constraint on rock
composition
Two Methods for Analyzing
Refraction and Reflection
Data
• Inverse modeling (tomography)
• Forward modeling
Refraction seismology
Inverse modeling
(tomography)
Refraction seismology
Forward modeling
Reflection seismology
Reflections
Reflections
should be here
should be
here
Conclusions
• 1. The crust is an important layer to image-perhaps the most important for
understanding Earth processes present and
past. Currently, Earthscope has no definite
plans or money to image the crust in a
systematic way.
• 2. Reflection profiling is the chief tool for
observing the crust.
Conclusions
• 3. We need, however, multidisciplinary
data collection, using all the methods of
investigation included in Complementary
Geophysics, to obtain the best constrained
understanding of lithosphere.
• 4. LITHOPROBE provides a good model
for how to proceed. (Ron Clowes did not
pay me to say this.)
Conclusions
• 5. Our COCORP "transects" of the 1970's
and 1980's need to be replaced with at least
one transect across the U.S. from margin to
margin, taking advantage of the tremendous
improvements in hardware and
software/processing since those days in
order to produce modern images like the
Canadians have done.