An insight to the Bucaramanga nest Zoya Zarifi, Jens Havskov and Anibal Ojeda* * Now at Ingeominas, Colombia ESC, September 2004

Tectonics of Colombia Dashed lines show surface trends of faults and plate boundaries. The arrows shows the movement of the Nazca plate (70 mm/year) and Caribbean plate (14 mm/year) relative to the South American plate.

Possible slab geometry for Colombian subduction

Station location of National Seismic Network of Colombia

Seismicity ISC data, 1964-2001 Local data, 1993-2000

Depth profiles in nest area Local data, 1993-2000 ISC data, 1964-2001

Profiles North of nest Dip of plate is around 25 degrees

Profiles South of nest Dip of plate is around 34 degrees

Profile on the entire local data set, which has chosen with the same criteria as before. It can be seen that the nest is located between the southern and northern slabs and it seems that the direction of subducting in the nest is more compatible with the southern slab.

Profile in the southern slab including the nest Profile in the southern slab including the nest. It can be seen that from the south towards the nest, the depth of shallower earthquakes is increasing. The direction of arrow shows the direction of increasing in depth

The profile in the northern slab including the nest The profile in the northern slab including the nest. It can be seen that from the north towards the nest, the depth of earthquakes is increasing. The direction of arrow shows the direction of increasing in depth

Magnitude as a function of location Latitude Longitude Depth

Fault plane solutions Harvard CMT solution in the area of interest from 1977 until present for the earthquakes deeper than 60 km. Fault plane solution

P and T-axis in nest area (Left) P- (Right) T-axis of stress in the area of the nest reported by Harvard CMT solution.

Energy distribution across the slab Energy distribution across the slab. The box shows the energy in the nest area. It can be seen that the deep earthquake in the nest area, based on both ISC and local data, has more energy release than any deeper part of slab and also more than the shallow part above the nest.