Arcila, M.

On the frame of The South America Risk Assessment (SARA) project, an earthquake catalogue was compiled for South America, in terms of the moment magnitude (Mw), with data from the Centro Regional de Sismología para América del Sur (CERESIS), recent national and international studies, and from the analysis conducted during the project. In particular, it is included the latest versions of catalogue CERESIS-91 prepared by CERESIS and published by the National Council of Science and Technology CONCYTEC of Peru, the determination of parameters by recent studies, including those proposed by the ISC-GEM catalogue, and where available, the national catalogues that meet the criteria of transparency required by the project. The results presented in this work correspond to the pre-1964 time window. The first phase of the study is the development of a critical inventory of all public studies related to earthquakes in South America. Studies for the same event have been associated with each other from the comparison of the time, of the epicentre coordinates and the size of the earthquake (magnitude or maximum seismic intensity). For each event, a set of parameters considered reliable has been preliminarily selected. The main problem of the catalogue is the need to express the values of magnitude in terms of moment magnitude (Mw). Currently, few studies on historical earthquakes provide this value for the study region. For many events, values in terms of Ms and mb are available; although for most cases, because of the time of occurrence of these events, the magnitude values were calculated from macroseismic data. For these earthquakes we have used empirical conversion relationships published in literature for Ms and mb to Mw. There are also events for which only a value of maximum intensity (Imax or Io) is available. For these events, regional relationships Imax to Mw have been determined, using the most reliable and recent data of Mw and Imax values. In a second phase, for some events that have a sufficient number of macroseismic data, the source parameters have (including location, Mw and uncertainties) been determined using the method of Bakun and Wentworth (1997), regionally calibrated, based on what already has been obtained for Ecuador, Venezuela in literature and Colombia in the present project. In this way, the magnitude Mw was evaluated for 2564 earthquakes in South America. The lower threshold is defined in Mw = 5 for the Andean region. For Brazil, a lower threshold was not applied.

Located in the extreme northwestern part of the Los Coconucos volcanic chain in the Central Cordillera, the Purace is one of Colombia's most active volcanoes. Recent geological studies indicate an eruptive history of mainly explosive behavior which was marked most recently by a minor ash eruption in 1977. Techniques used to forecast the renewal of activity of volcanoes after a long period of quiescence include the monitoring of seismicity and ground deformation near the volcano. As a first approach toward the monitoring of the Purace volcano, Southwest Seismological Observatory (OSSO), located in the city of Cali, set up one seismic station in 1986. Beginning in June 1991, the seismic signals have also been transmitted to the Colombian Geological Survey (INGEOMINAS) at the Volcanological and Seismological Observatory (OVS-UOP), located in the city of Popayan. Two more seismic stations were installed early in 1994 forming a minimum seismic network and a geodetic monitoring program for ground deformation studies was established and conducted by INGEOMINAS.