Receiver sheet

In this sheet (Fig.below) you may access the specification concerning the receiver position both with respect to its coordinates as well as to its position within the layer stack. The coordinates are entered in the frame named “Receiver position”. There are two text boxes where the coordinated expresses in UTMX and UTMY can be edited. As in the “Source” sheet, UTMX and UTMY are metric coordinates as in systems like, e. g, Gauß-Krüger or Gauß-Boaga.  SHAKYGROUND calculates the epicentral distance of the receiver and displays it in the frame “Epicentral distance” in the box labeled with “Calculated (m)”. Since the epicentral distance results automatically from the source and receiver coordinates it cannot be edited. What can be done, however, is to subject the epicentral distance to a random fluctuation in the same way as is done for the source and layer parameters. In the spin-box (box with the double horizontal arrow) the user specifies the bandwidth of the random fluctuation in percent of the value calculated. In other words, if the calculated epicentral distance is 10,000 m and the user specifies a random fluctuation of 15% then the actual epicentral distance used during the simulations will float around the calculated one according to a standard deviation of ± 1500 m. SHAKYGROUND reports the absolute value of the fluctuation in a text-box, where, however, editing is disabled. Note that in the concept of SHAKYGROUND the receiver position is linked with the layer stack which are actually present on the “Strata” sheet. If a geological model is loaded from the catalog, SHAKYGROUND automatically loads also the corresponding receiver position linked to that layers. If you wish to save the receiver coordinates (and its vertical position within the layer stack) you have to do this using the “Strata” sheet (click the “Strata” sheet then “Save in Catalog”). Or you may use the option to save the whole model, i. e., the whole bunch of the 6 sheets, by clicking the floppy-disk icon on the toolbar underneath the title “Models”.

Finally SHAKYGROUND offers on option to consider the wave field in some depth instead of a position directly on the earth’s surface. This option can be useful if the foundations of a building are situated at some depth. The seismic loading at depth is often lower due to destructive interference of upgoing and downgoing waves. In the frame “Receiver position within layer stack” SHAKYGROUND permits to pose the receiver at one of the layer interface of the geological model. SHAKYGROUND displays the model schematically. The first position is the “Surface” which is also the default. Clicking one of the subsequent layer names moves the receiver to the lower boundary of that layer. At a first glance there seems to be a limitation since the receiver position is linked to a layer boundary. This limit, however, can be easily circumvented by the creation of a virtual layer subdividing an existing layer into two layers with identical impedance and Q values, and choosing the thicknesses appropriately. Note again that the receiver position can be saved totgether with the layer parameters using the “Strata” sheet, or by saving the “Mode”, i. e. the whole stack of SHAKYGROUNDs input sheets.

The Receiver Sheet with coordinates, and the vertical position within the layer stack.