Key result
Download
1 / 89

Key Result - PowerPoint PPT Presentation


  • 187 Views
  • Uploaded on

Seismic CAT Scan. Key Result. vs. Trenching. Seismic CAT Scans of Ancient Earthquakes in Utah. Dave Morey, Dave Sheley and Jerry Schuster University of Utah. Outline. Paleoseismology Seismic CAT Scan Idea Results: Conclusions. Oquirrh Fault Wasatch Fault. Paleoseismology.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Key Result' - mrinal


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Key result l.jpg

Seismic CAT Scan

Key Result

vs

Trenching


Seismic cat scans of ancient earthquakes in utah l.jpg

Seismic CAT Scans of Ancient Earthquakes in Utah

Dave Morey, Dave Sheley and Jerry Schuster

University of Utah


Outline l.jpg
Outline

  • Paleoseismology

  • Seismic CAT Scan Idea

  • Results:

  • Conclusions

Oquirrh Fault

Wasatch Fault


Paleoseismology l.jpg
Paleoseismology

  • Determine Earthquake Hazard


Paleoseismology5 l.jpg
Paleoseismology

  • Determine Earthquake Hazard

  • Trenching Studies: estimate size and recurrence intervals of ancient earthquakes from the thicknesses and separations of colluvial wedges







1000 years later l.jpg

Colluvial Wedge

1000 Years Later


1000 years later12 l.jpg
1000 Years Later

Colluvial Wedge

Thickness = Earthquake Magnitude


2000 years later l.jpg
2000 Years Later

2 Colluvial Wedges

Separation = Recurrence Interval


Trench wedge l.jpg

Trench & Wedge

Trench Colluvial Wedge


Slide15 l.jpg

RECENT UTAH EARTHQUAKES

12000 ft

Magnitude

Elevation

6.5

4.5

4100 ft





Slide19 l.jpg

}

16 earthquakes/5600 yrs

5 segments

10 Fault Segments: 300-400 Year Recurrence Intervals


Trenching problems l.jpg
Trenching Problems

  • Trenches are:

    • Expensive

    • 2-D

    • Shallow

Megatrench Trench


Outline21 l.jpg
Outline

  • Paleoseismology

  • Seismic CAT Scan Idea

  • Results:

  • Conclusions

Oquirrh Fault

Wasatch Fault


Seismic imaging of colluvial wedges l.jpg
Seismic ImagingofColluvial Wedges


Seismic imaging of colluvial wedges23 l.jpg
Seismic ImagingofColluvial Wedges


Seismic imaging of colluvial wedges24 l.jpg
Seismic ImagingofColluvial Wedges

Fast Time


Seismic imaging of colluvial wedges25 l.jpg
Seismic ImagingofColluvial Wedges

Slow Time

Fast Time

Colluvial Wedge


Seismic imaging of colluvial wedges26 l.jpg
Seismic ImagingofColluvial Wedges

0.5-1.0 m





Many traveltime equations for each shot l.jpg
Many Traveltime Equations for Each Shot

T = L /v + L /v + L /v

T = L /v+ L /v + L /v


Outline31 l.jpg
Outline

  • Paleoseismology

  • Seismic CAT Scan Idea

  • Results:

  • Conclusions

Oquirrh Fault

Wasatch Fault


Slide32 l.jpg

Oquirrh Fault Scarp

Trench

3-D Seismic

Array

Oquirrh Mountains

12000 ft

Elevation

4100 ft








Slide39 l.jpg

2.5’

140’

5’

40’

Oquirrh Mountains


Seismic data l.jpg
Seismic Data

100,000 Traveltimes

TIME

20,000 Unknowns

Multigrid SIRT

OFFSET



X z slice of the 3 d tomogram at y 10 ft l.jpg

X-Z Slice of the 3-D Tomogram

15 ft

20 ft

X-Z Slice of the 3-D Tomogram at Y=10 ft


Comparison with adjacent trench l.jpg

11.2 ft

Comparison with Adjacent Trench




Outline46 l.jpg
Outline

  • Paleoseismology

  • Seismic CAT Scan Idea

  • Results:

  • Conclusions

Oquirrh Fault

Wasatch Fault



Slide48 l.jpg

Megatrench Survey(Sheley & Crosby)

Megatrench Site

2-D Seismic Line

12000 ft

Elevation

4100 ft


Slide49 l.jpg

F4

F1

MCCALPIN’S MEGATRENCH


Trench log l.jpg

0

3m

3-4 events

11

27

0

Trench Log

F1

F4

Depth (m)

Offset (m)

Bonneville

12-15 ca


Seismic trenching l.jpg

Megatrench Site

Seismic Trenching

2-D Seismic Line

0.5 m src/rec Interval

168-chan., 40 Hz geo.

> 27 K traveltimes



Velocity tomogram l.jpg

0

Offset (m)

40

0

120

Velocity Tomogram

Depth (m)

0

400

1400

1800

Velocity (m/s)


Velocity tomogram54 l.jpg

Bonneville

0

Offset (m)

40

0

120

Velocity Tomogram

?

Depth (m)

0

400

1400

1800

Velocity (m/s)


Summary l.jpg

  • New Paleoseismic tool: Seismic tomography can be an alternative/complement to the intrusive task of fault trenching.

Summary

  • First time colluvial wedges have been imaged with seismic method


Summary56 l.jpg

  • Seismic Megatrench Images suggest

    Arrythmia beyond 15,000 years ago.

    Does lake act as a wedge eraser?

    Was it also quiet along F1?

Summary

No dates

Sesmic wedge, 1 event or several?

3-D certainty > 2-D certainty


Future work l.jpg
Future Work providing

  • Apply method to other faults.

  • Dig and date colluvial wedge --> recurrence interval as well as the magnitude.

    Wave equation traveltime tomography


Possible solution l.jpg
Possible Solution providing

  • Use 3-D refraction traveltime tomography to image colluvial wedges


Slide60 l.jpg

TOMOGRAM providing

1.8 km/s

0 km/s

0

40

0

120

MIGRATION SECTION

0

40

0

120

Offset (m)


3 d seismic survey l.jpg
3-D Seismic Survey providing

50

40

30

In-line Station Number

20

10

0

1

2

3

4

5

6

7

Cross-line Number


2 d seismic line l.jpg
2-D Seismic Line providing


Outline64 l.jpg
Outline providing

  • Paleoseismology

  • Seismic CAT Scan Idea

  • Results:

  • Conclusions

Oquirrh Fault

Wasatch Fault


3 d traveltime tomography l.jpg
3-D Traveltime Tomography providing

Data Misfit Function

Model Updating Direction



Seismic data inversion l.jpg
Seismic Data & Inversion providing

100,000 Traveltimes

TIME

20,000 Unknowns

Multigrid SIRT

OFFSET


Results l.jpg
Results providing

  • Synthetic Results

  • 3-D Traveltime Tomography Results

  • 2-D Reflection Results



3 d tomography results l.jpg
3-D Tomography Results providing

0.045

0.04

0.035

0.03

RMS Residual (s)

0.025

0.02

0.015

0.01

2

4

6

8

10

12

14

16

18

Iteration Number


Slide71 l.jpg

Goal providing

Use traveltime tomography to image colluvial wedges


Reflection results72 l.jpg
Reflection Results providing

CMP Number



Parameters used to calculate net vertical tectonic displacement l.jpg
Parameters Used to Calculate Net Vertical Tectonic Displacement

  • Tm=22.8 ft (Tomogram)

  • W=169 ft (Migrated Seismic Section)

  • =4 degrees (Migrated Seismic Section)

  • Ta=4.3 ft (Migrated Seismic Section)

Tnet=6.7 ft


Calculation of paleoearthquake magnitude l.jpg
Calculation of PaleoEarthquake Magnitude Displacement

Regression Equation

M = 6.61 + 0.71 * log(Tnet)

Paleoearthquake Moment Magnitude = 6.8

Compared to moment magnitude of 7.0

calculated from the trenching study


Limitations l.jpg
Limitations Displacement

  • Less resolution 2-3 ft vs < 1ft

  • More uncertainty than trench studies (will I get a good image??)

  • No direct dating


Reflection method l.jpg
Reflection Method Displacement


Reflection method78 l.jpg
Reflection Method Displacement


Reflection method79 l.jpg
Reflection Method Displacement


Reflection method80 l.jpg
Reflection Method Displacement


Reflection method81 l.jpg
Reflection Method Displacement


Reflection method82 l.jpg
Reflection Method Displacement




Slide85 l.jpg

dx = Displacement

/2

Intersection of Fresnel Zones

sin /4

dz =

Tomographic Resolution

Intersection of Wavepath Fresnel Zones



Slide87 l.jpg

WASATCH FAULT TOMOGRAM Displacement

(Hidden Park)

0’

35’

0’

35’

600’/s

600’/s

0’ 35’

520’/s

520’/s

0’

2500’/s

150’

0’/s

0’

150’

0’ OFFSET

200’


Slide88 l.jpg

WASATCH FAULT TOMOGRAM Displacement

(Hidden Park)

600’/s

0’

20’

520’/s

0’ 50’

0’

2500’/s

150’

0’/s

0’

150’

0’ OFFSET

200’



ad