The RESNOM seismic catalog and its bearing on the seismicity of Northwestern Mexico

Abstract

The catalog of the Red Sísmica del Noroeste de México (RESNOM) operated by CICESE is investigated. Probable artificial effects are detected. Current values for the minimum magnitude of completeness (M_c) and its spatial variations are outlined. Significant changes in reporting were found during early 1987, mid 1992, and early 1997. By inspecting the bulletins for 1987 to 1992 we found that the rate of located to recorded events was close to 50%. Comparing cumulative and non cumulative rates for 1987 - 1992.4 with 1992.4 - 1997.11 there is a difference of about 60% in the trends of located events. The difference is greater in the region of maximum resolution of the network. The change for the period 1992.4 to 1997.11 as compared to 1997.11 to 2001.5 does not warrant a correction; however, the number of events with duration magnitude M_d≤ 3.5 reported during the most recent interval is 38% larger than for the preceding period. Magnitudes calculated by RESNOM (M_d) and PDE (m_b) match if the magni tudes reported by RESNOM are increased by 0.1. The same correction should be applied when merging data from RESNOM with SSN. The minimum magnitude of completeness for current reporting is 2.4 Some areas with good coverage, in particular around 32°N and 116.5°W, can detect magnitudes as low as 1.6. The resolution of the network in some areas has improved considerably, with M_c decreasing as much as 1 magnitude unit.