“Did we detect that LARGE global earthquake? Maybe it’s “not there”…..I just observe noise”. On May 14th, 2019, a MAJOR magnitude M7.5 earthquake hit Papua New Guinea. Here in Spring, TX, operated by Texas Educational Seismic Project, the ground motion was detected very obviously on the EQ1 educational seismograph (see Figure 1a). On site, we also have a Raspberry Shake seismograph which we hoped had an equally observable response to the massive earthquake (Figure 1b). Due to mechanical and technological differences between the instruments, we did **not** see the response on the RS. Or did we?
For over a year, TXESP (and others) have been carefully reviewing the technical capabilities of the Raspberry Shake seismographs compared to different educational seismographs (EQ1, AS1). One of the most important concepts we are continuously learning is the application of filtering data. In signal processing, a filter is a device or process that removes some unwanted components or features from a signal. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal.
Compare the un-filtered / filtered images (Figures 2a/b and 3a/b) – they now appear more similar to each other and we can “easily” see the earthquake recorded by both instruments.