# Proposal for a System Model for Offline Seismic Event Detection in Colombia
## 4 Seismic Detection Model Proposal
### Analysis of Seismological Stations  
Once the historical seismic archives are read, an analysis of the seismological stations that have recorded the events of interest is carried out, so that those that best represent the events and allow a reduction of the computational load in the processing of the data can be selected. The selected seismological stations are obtained as an output of this process. Figure 3: Seismic data cleaning process for RSNC files. Each seismic station provides a specific recording pattern that is dependent on several factors:  
* The distance from the hypocenter and the epicenter (hypocenter and epicenter distances) to the geographic position of the station defines the amount of attenuation of the seismic wave. * The geomorphology to which the seismic waves are exposed on the way to the station defines the propagation pattern and the attenuation of the seismic waves. * The natural and artificial noise sources demean the seismic records due to the loss of quality regarding the content associated with seismic information, adding sources of information that concern other events that are not from a seismic nature. * The technical parameters of the stations such as measurement channels, signal-to-noise ratio, analog-to-digital conversion, sampling rates, sensitivity, and dynamic range define how the seismic event is perceived from an analog source to a digital environment. Then, these factors influence the composition and patterns of the traces that are transmitted to the monitoring site and stored for further offline processing. Each Colombian station records the seismic events individually by considering the named factors. The more stations that detect the event, the more data that can be transmitted, processed, and stored. When a microseism occurs, usually few stations record it, since it can be a noise event due to a local disturbance on the surface or a seismic event of very low magnitude and/or considerable depth. In this case, the amount of data that contains useful information is not extensive and can be analyzed quickly and stored without major physical space costs. However, when there are long-term, shallow, or large-scale seismic events that are perceived in various regions, the computational capacity for analysis and storage is high. Therefore, selecting a set of stations to analyze the traces that are recorded allows the dimensionality reduction of the data and reduction of the computational load. Defining the stations to be studied is a process that requires a strong seismological criterion; however, the use of algorithms for statistical analysis facilitates the discernment between station selection criteria. For example, using libraries for the geographical mapping of stations and seismic epicenters, clustering and sampling the data exposed in the parameter files, among other procedures, allow contrasting the information stored and decide about the stations that best represent the events analyzed. Figure 4 proposes a general procedure for the selection of the seismological stations used to identify the presence of seismic events in the Colombian monitored signals. At first sight, it is necessary to identify the geo-referenced position of the stations, so that there is a spatial perspective of their distribution. Depending on the area under monitoring, the stations of interest will be those closer to this area. This is because the dynamics of local earthquakes are more marked and detectable than the dynamics of regional earthquakes and teleseisms, which have  
Figure 4: Seismological station selection process. attenuated and difficult to model features. It is recommended that more than two stations be selected, as events that have a non-seismic nature can be detected as such if only the activity is monitored in one or two stations. In the second stage, it becomes clear to calculate the identification rate of seismic events labeled by each station, according to the monitoring region.