# Proposal for a System Model for Offline Seismic Event Detection in Colombia
## 4 Seismic Detection Model Proposal
### Sample Selection  
The sample selection process can be carried out in parallel to the station analysis process, since these two processes are independent of each other. There are several factors to consider when selecting a Colombian seismic event sample, as it was shown in Section 4.2:  
* Inconsistencies in the file formats: There are different formats in which a seismic file can be structured, as SEED and miniSEED. During the processing and storage stages, the data are susceptible to be modified or lost, since there are multiple sources of information. Sometimes, these modifications alter the file formats, making them inconsistent. The files that present inconsistencies in the format and cannot be read correctly must be discarded.
* Absence of trace files that correspond to SEED and SAC existing parameter files: As part of the data storage process, the seismic information extracted from the seismic events (Sfiles) and the seismic samples (Waveforms) are recorded in separate files, as described in previous sections. Some of them are stored as part of the dataset without being associated. In this way, cases in which seismic information is recorded and samples were lost and vice versa can be found. Those files where the description data do not correspond to the seismic traces must be discarded.
* Lack of start and end times and/or inexistence of P-wave and S-wave arrival times in the events recorded: when a seismic event is recorded, some variables are measured, among which are the start time and end time of the event and the P-wave and S-wave arrival times. These values are very important to train classification algorithms, as some specific samples can be extracted from the seismograms, knowing when the earthquake began and when it finished. Unfortunately, some files can be well stored but lacking one or more of these four key parameters. In this case, it should be analyzed whether it is possible to determine the start or end date of the event by processing the seismic traces. If this is not possible, the files must be discarded.  
It is also important to consider the structural changes of the stations, such as changes in the sampling frequency, sensors, digitizers, and number of spatial components, among others. These variations, although some of them are subtle, represent substantial alterations in the seismic patterns that might not be detected, since the detecting algorithms learn from specific patterns shown in the learning stages.  
The inconsistencies in the files may be a consequence of the wrong acquisition, processing, and storage processes that are sometimes attributable to the algorithms that execute those processes for the seismology entities of each region or country.  
In Colombia, between 20% and 30% on average of the selected files within the initial population of seismic events are propense to be discarded due to these inconsistencies, although some regions that are affected by very strong seismic events have accurate and well-stored files [41]. Other less frequent irregularities that may occur are (a) recording of the seismic data from stations that are inactive, (b) recording of the seismic data from components that the seismological station does not have (e.g., the registration of three components for stations with monoaxial sensors), (c) recording seismic traces with a different sampling frequency from that described in the sensor datasheet, (d) recording of the seismic traces with different sampling frequencies among the components from the same station, either by components or by events, (e) the annotation of the P-wave in the traces is outside the measurement period of the seismic events, and (f) recording of all relevant seismic attributes described of the seismic signals with a magnitude of zero.