Earthquake Magnitude Relationships for the Saint Peter and Saint Paul Archipelago, Equatorial Atlantic

We have investigated several relationships between ML, M(NEIC) and Mw for the earthquakes locally recorded in the Saint Peter and Saint Paul Archipelago (SPSPA), Equatorial Atlantic. Because we only have one station in the area, we could not derive attenuation relations for events recorded at different distances at different stations. Our approach was then to compare our ML estimates with magnitudes reported by NEIC. This approach produced acceptable results particularly for epicentral distance smaller than 100 km. For distances greater that 100 km, there is a systematic increase in the residuals probable due to the lack of station correction and our inability to accurately estimate Q. We also investigate the Mw—M(NEIC) relationship. We find that Mw estimates using S-wave produce smaller residuals when compared with both M(NEIC). Finally, we also investigate the ML—Mw relationship and observe that given the data set we have, the 1:1 holds. We believe that the use of the present methodologies provide consistent magnitude estimates between all the magnitudes investigated that could be used to better assess seismic hazard in the region.