1. A. Ghosh, EAS, Georgia Tech Distribution of b-value in the Middle America Trench, near Nicoya Peninsula, Costa Rica Abhijit Ghosh A. V. Newman, A. M. Thomas, G. T. Farmer School of Earth & Atmospheric Sciences Georgia Tech

2. A. Ghosh, EAS, Georgia Tech Outline of the talk Basics of plate tectonics Why this study is important What is b-value… Data processing and results Discussions Summary

3. A. Ghosh, EAS, Georgia Tech Plate tectonic map http://earthquake.usgs.gov/

4. A. Ghosh, EAS, Georgia Tech Plate boundaries http://www.permatopia.com/wetlands/images/

5. A. Ghosh, EAS, Georgia Tech Why this study is important Lowman and Montgomery, 1998

6. A. Ghosh, EAS, Georgia Tech Study area: Middle America Trench

7. A. Ghosh, EAS, Georgia Tech Earthquake catalog

8. A. Ghosh, EAS, Georgia Tech Seismic network and earthquake location 1-D global velocity model3-D local velocity model

9. A. Ghosh, EAS, Georgia Tech What is ‘b-value’… : frequency- magnitude distribution log 10 N = a – b. M M = Magnitude of earthquakes N = number of earthquakes equal or greater than M b = slope of the line a = intercept of the line (seismicity rate)

10. A. Ghosh, EAS, Georgia Tech b-value in the study area b = 1.29±0.03 a = 6.19±0.1

11. A. Ghosh, EAS, Georgia Tech Spatial variation of Mc

12. A. Ghosh, EAS, Georgia Tech Spatial variation of b-value

13. A. Ghosh, EAS, Georgia Tech b-value error

14. A. Ghosh, EAS, Georgia Tech Interpretation Norabuena et al., 2004

15. A. Ghosh, EAS, Georgia Tech Summary b-value varies spatially in the Middle America Trench (MAT), near Nicoya Peninsula Anomalously low b-value zone detected May indicate locked part of MAT Supported by independent geodetic model b-value mapping may be used to identify locked portion of subduction zone

16. A. Ghosh, EAS, Georgia Tech