# Proposal for a System Model for Offline Seismic Event Detection in Colombia
## 4 Seismic Detection Model Proposal
### Seismic Data Seeking and Gathering  
To analyze seismic signals by algorithmic means, it is necessary to have a set of records that can be manipulated. In this first step, a download of the historical seismic records is made, filtering by the chosen region. A set of seismological records of each station is obtained.  
Depending on the region of interest, it is possible to obtain seismological records through web services, such as the United States Geological Survey (USGS), the European-Mediterranean  
Figure 2: Model for offline seismic event detection.  
Seismological Centre (EMSC), the National Earthquake Information Center (NEIC), the National Institute of Seismology, Volcanology, Meteorology, and Hydrology of Guatem (INSIVUMEH), the Mexican National Seismological Service (SSN), the National Seismological Center of Chile (CSN), or the Colombian National Seismological Network (RSNC by its Spanish acronym), among others. These web services allow downloading data of seismic events one by one, although it is usually necessary to provide searching filters, generally concerning magnitudes, depths, and dates.  
The seismic records are usually of public access, so it is possible to request the set of desired data directly to the seismology agency responsible for its storage. Another easier way to do this data-gathering process is to use automated interaction web tools to download the requested files, such as the creation of web snippets using the web-scraping technique, which allows interacting with the web resources of the web service. This technique is usually legally authorized by the RSNC and other services, since all the information downloaded is public access and no intromission for non-authorized domains or web resources is made. Although the scraping procedure is legally accepted, it is recommended to inform the geological services about this practice when executed.  
The technological infrastructure needed to download and to store seismic files depends on the volume of data to be processed. In Colombia, the RSNC gathers the seismic records into two categories:  
* Trace files (Waveforms), which contain the seismic samples taken by all seismological stations available around the region of interest.
* Parameter files (Sfiles), which provide detailed information about the seismic events, such as the longitude and latitude of the epicenter and the P-wave and the S-wave arrival times, among others.  
The seismic traces recorded in the Waveform files are usually a large size because they record non-event samples that occur before and after the seismic event picking. Their content is dependent on the duration of the recorded earthquake. Each trace file can have a storage size from approximately 5 MB if it corresponds to a microseism that has been registered by one or few seismological stations, or a specific seismic event registered by a couple of stations, and up to approximately 120 MB, if it is registered by most seismological stations with a duration close to five to ten minutes. The RSNC registers up to 10,000 seismic events per year, with an average of 60 MB of storage per seismic record.  
The seismic records may not be stored completely. The storage of all the records allows faster access for later processing stages; however, as has already been shown, the computational load applied to the data storage is high. On the other hand, storing portions of data that are processed and then erasing the unrequired portions, or processing the records one by one so that the results are stored and the records are erased are two recommended procedures to save storage space. Nevertheless, if the data are processed one by one, any subsequent processes to be done or corrections to previous processes will force to access the data sources again, which will hinder processing.