A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx...
Transcript of A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx...
![Page 1: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/1.jpg)
![Page 2: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/2.jpg)
Outline
• Background informa3on on Magne3c Anomalies
• Deriva3on of a Model
• Fi:ng the Model to Spreading Ridge Data
![Page 3: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/3.jpg)
How are Magne3c Anomalies formed?
![Page 4: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/4.jpg)
What are we measuring?
![Page 5: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/5.jpg)
What are we measuring?
![Page 6: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/6.jpg)
Magne3c Anomalies give a 3mescale for the seafloor going away from the ridge.
![Page 7: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/7.jpg)
Half magne3c anomaly
![Page 8: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/8.jpg)
10my full magne3c anomaly
![Page 9: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/9.jpg)
How do we measure the magne3c field at sea?
total magne3c field = magne3c field (earth) + magne3c field (anomaly)
We measure the magnitude of the total field.
measured scalar anomaly
![Page 10: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/10.jpg)
![Page 11: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/11.jpg)
What causes the differences between the observed anomaly and the magne3c polarity
3mescale?
• Earth filter -‐ smoothed by depth
• Skewness -‐ due to magne3c field inclina3on
• Superposi3on -‐ due to slow spreading rate
![Page 12: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/12.jpg)
Effect of depth (earth filter):
Arbitrary horizontal units
200 2000
4000
Magne3c Anomaly (nT)
![Page 13: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/13.jpg)
Effect of inclina3on (skewness): De
grees o
f skew/
Magne
3c Ano
maly
Arbitrary offset
![Page 14: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/14.jpg)
Limits of model resolu3on (superposi3on):
![Page 15: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/15.jpg)
Modeling the Magne3c Anomalies
![Page 16: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/16.jpg)
Modeling the Magne3c Anomalies
![Page 17: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/17.jpg)
Modeling the Magne3c Anomalies
No change in the y direc3on.
![Page 18: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/18.jpg)
Modeling the Magne3c Anomalies
Assume that this spreading ridge is located on the magne3c pole.
![Page 19: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/19.jpg)
Modeling the Magne3c Anomalies
Only the z component of the Earth’s magne3c field is non-‐zero.
reversal paZern x earth filter
![Page 20: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/20.jpg)
Modeling the Magne3c Anomalies The spreading ridge is not at the magne3c pole; this introduces a phase shi] θ.
![Page 21: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/21.jpg)
Modeling the Magne3c Anomalies
• A-‐ scalar magne3c anomaly (T) • k-‐ wave number 1/λ (m-‐1) • zo-‐average seafloor depth (m) • θ-‐ skewness • C-‐unknown constant • μo-‐magne3c permeability=4π10-‐7 • p(k)-‐ fourier transform of magne3c 3mescale
![Page 22: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/22.jpg)
Modeling spreading rate
Distance from spreading center
![Page 23: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/23.jpg)
Mid Atlan3c Ridge
![Page 24: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/24.jpg)
MAR spreading rate and skew Spreading rate:
13500m/my Skew: -‐15 degrees
![Page 25: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/25.jpg)
Pacific-‐Antarc3c Ridge
![Page 26: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/26.jpg)
Pacific-‐Antarc3c Ridge Spreading rate:
46500 m/my Skew: 20 degrees
![Page 27: A magnetic anom - University of California, San Diego · 2011. 10. 28. · A_magnetic_anom.pptx Author: David Sandwell Created Date: 10/28/2011 5:08:09 PM ...](https://reader036.fdocuments.in/reader036/viewer/2022071509/612d21111ecc51586941ff45/html5/thumbnails/27.jpg)
Ques3ons?