Low Level Services

Low Level Services are distinguished from High Level Services because they perform relatively simple data transformations, resulting to data as well. On the contrary, High Level Services perform specific analyses and methods, utilizing data in order ti produce more sophisticated results, not just simple data elaboration/transformation. The Low Level Services available in the IS-EPOS web platform, are described in this section:

Seed response calculation
Seismogram picking tool
Catalog Filter
Coordinates Transformation
Magnitude Conversion
Signal download tool
Waveform Download tool
Time-Series tool

Description of Low-Level Services:

Seed response calculation

This service uses seed files (uploaded from change input icon, Figure 1) as input, to extract from them the time series corresponding to a selected response unit. The User may select among "Displacement", "Velocity" and "Acceleration" from the tab next to "Response Unit" field as shown in Figure 1, and then click on the "Run" button (Blue button in Figure 1).

Figure 1.

A new file has been now created and can be accessed by clicking on one of the two links shown in red frames shown in Figure 2:

Figure 2.

After this selection the window shown in Figure 3 appears in the screen. A interactive geographical map with the locations of the seismic network station depicted is demonstrated (also see "maps guide" section in "Visualizations" chapter). Moreover, the waveforms from the signals recorded by those stations (3 channels - E, N, Z) are available, corresponding to the response unit (Displacement, Velocity, Acceleration) previously selected by the User (also see "Waveform viewer guide" section in "Visualizations" chapter for waveform processing). The User can now use these waveform data for further analysis by selecting one of the available applications (actions) as shown in the top left corner of Figure 3.

Figure 3.

Seismogram picking tool

Seismogram picking tool takes as input seed files. The service interface is identical to the one shown in Figure 3. Here the User can pick phases or points from the given waveforms (also see Waveform "Viewer guide" section in "Visualizations" chapter). Once the picks have been chosen, the User may proceed to further analysis by clicking the blue "Run: button (blue button, Figure 4.). The number of picked phases are counted by the system. The User can now recall the output file (.xml, shown into the red frame, at the bottom of Figure 4), for any Waveform-based application (i.e. Moment Tensor Inversion, Earthquake Spectra, Source Location)

Figure 4.

Catalog Filter

This is a service for filtering seismic catalogs. The product is a new catalog filtered upon the User's parameters setting. The input file is a seismic catalog that can be uploaded from "Change Input" tab (shown in the yellow frame of Figure 5). Next, the User may perform various filtering according to the values of the attributes assigned in the catalog. The User may choose one of these attributes (as ID, ML, Lat etc, displayed in Figure 5) and provide the values he/she wishes, selecting among 'Select all values' (option "1", Figure 5), 'Select Range' (option "2", Figure 5) and 'Select list of values' (option "3", Figure 5).

Figure 5.

Alternatively, the User may apply interactively spatial filtering by clicking in the "Select events from map" tab (depicted by the red box in Figure 5). This option grants to the User the possibility to select data, spatially constrained by a predefined shape (numbers 2-4 in Figure 6):

1) No draw option.

2) Draw a polygon.The User may select data into a polygon drawn after clicking on different points of the map. To close the polygon, the User has to double click on the last point, such that this point will be connected with the first one.

3) Draw a rectangle. To select data into a rectangular the User has to click on a point of the map and move the cursor to any direction. A second left mouse button click will restrict the selected area at its current state.

4) Draw a circle (option demonstrated in Figure 6). To select data into a circular the User has to click on a point of the map and move the cursor to any direction. A second left mouse button click will restrict the selected area at its current state. Note that the first click on the map defines the circle's center.

Figure 6.

As soon as the filtering criteria have been defined, the User shall click on the "Run" button (blue button at the bottom of Figure 5) to apply the those criteria. The User may also select the "Preview Selection on map" tab (indicated by the green frame, at the bottom of Figure 5) in order to view an illustration of the events from the original catalog (red circles) and the events included in the filtered catalog (green circles). A new catalog (catalog.mat) has been created and it is available for any further processing. In addition the system provides all the information and services that are valid for the original catalogs (see "AH Episodes" Chapter, for details).

Coordinates Transformation

This Application is performed in order to transform the epicentral location of the seismic events into a selected Cartesian Coordinate System (Note that epicentral location data available in IS-EPOS is given in geographical coordinates). The available types of coordinate systems are shown in Figure 7. Once the User makes the selection and clicks on the "Run" button, a new catalog is created, which contains all the data previously available in the original catalog, plus the seismic events epicentral location in the selected Cartesian system. The new catalog is stored in the platform and is available for any further processing. In addition IS-EPOS provides all the information and services that are valid for the original catalogs (see "AH Episodes" Chapter, for details).

Figure 7.

Magnitude Conversion

Magnitude Conversion is a service used for establishing linear relationships between different magnitude scales, which can be later used for conversion of magnitudes from one scale to another. The input file is the seismic catalog that can be uploaded from "Change Input" tab (shown in upper right corner of Figure 8). The Service can be performed only in datasets in which more than one magnitude scale is assigned for the seismic events (e.g. ML and Mw). The parameters that the user has to set/choose are also shown in Figure 8:

Figure 8.

Choose first vector to compare: The user may choose among the different magnitude scales available in the catalog.
Choose second vector to compare: The user may choose among the different magnitude scales available in the catalog.
Regression Method: Three different regression methods can be used - General Orthogonal Regression, Standard Least Squares and Inverted Least Squares.
Error Variance Ratio: A float number should be assigned here (default is 1). Note that this option is only valid when General Orthogonal Regression method, is chosen.

The outputs that the service produces are:

A report with the parameters (slope and intercept) of the regression process and some associated statistical parameters (Figure 8)
Vectors of the first, second magnitude selected, together with the vector of the new (converted) magnitudes obtained by the application of the regression equation.
A figure with one magnitude scale plotted versus the other one (scatter plot) and the linear regression curve (Figure 9). Zooming option is enabled for this Figure.

Figure 9.

Signal download tool

This services extracts seed files and event files from a selected catalog into the User workspace. These extracted files can be used later on at any service dealing with waveform processing, including Spectral Analysis, Source Location, Moment Tensor Inversion and Seed response calculation. This is an alternative way of exporting seed files instead of searching into the episode database. The User needs first to select a catalog from the workspace and click subsequently on ACTIONS, USE IN SERVICE and Signal download tool tabs, as indicated by the red boxes in Figure 10.

Figure 10.

After this step, the list of events appears in the screen as shown in Figure 11 and the User is requested to select an event for extracting event information and seed file. The User may also chose downloading between Seed Signal, Accelerogram Seed Signal, or All, by ticking on the respective box shown at the bottom left corner of Figure 11.Then, the output files are extracted after clicking on the RUN button (green button, bottom Figure 11). Those files are stored in a Signal Download folder, into the User's workspace and can be further used as input in several services as mentioned above.

Figure 11.

Waveform Download tool

This application allows for ordering parts of continuous waveforms for specific dates and stations as processed by Seiscomp. The User needs to upload the application from the low-level services repository to the personal workspace. The preparation of the waveform is executed by Arclink-fetch. The User has to select the respective episode and time period of interest, as shown in Figure 12). For selection of the the time period the User may either set values to the 'Start' and 'End' point, or specify the 'Start' point and the duration (length) of the periods he/she wishes to study. After this the User selects among the channels and the stations available for each episodes and cliscs on "RUN" button. A *.seed file is soon to be created, and it can be furthered processed within other applications, such as, FOCI, Waveform Analysis or Seismogram picking tool.

Figure 12.

Time-Series tool

This application is used to select appropriate time series from the cumulative events distribution plot. The User uploads the catalog of interest from the personal workspace (change file tab - Figure 13). Then, after clicking on "SHOW PLOT" tab, the starting and ending points of the period of interest are selected by clicking on certain points of the cumulative events curve (Figure 14). Running the application, creates a time series matlab file, which can be downloaded, plotted, or used in further processing of time series in particular by the following applications belonging to "Correlation Analysis application package (Technology-seismicity interaction):

Autocorrelation
Cross correlation
Coefficient of randomness
Priestley-Subba Rao (PSR) Test

Figure 13.

Figure 14.