Detecting events in the urban seismic wavefield using a novel nodal array in Singapore: earthquakes, blasts and thunder quakes

TitleDetecting events in the urban seismic wavefield using a novel nodal array in Singapore: earthquakes, blasts and thunder quakes
Publication TypeJournal Article
Year of Publication2020
AuthorsLythgoe KH, Loasby A, Wei S
JournalJournal of Geophysical Research - Solid Earth
Abstract

Receiver density is key to being able to detect and characterise seismic events at the noise level. This is particularly important in urban environments where high cultural noise levels can obscure seismic event signals at a single station. Here we catalogue the seismicity and describe the basic data features of a dense nodal array that was deployed in the city state of Singapore for a 1 month period in 2019. We utilise array methods to detect and characterise seismic events, the first based on waveform similarity (Li et al 2018) and the second (presented here) on spectral energy. Distant earthquakes are easily detected using the waveform similarity method, but local events are more difficult to detect in this way. We therefore develop a spectrogram stacking approach that highlights the location of anomalous coherent spectral energy. Overall, we identify 76 distant earthquakes and 35 local events. Out of the local events, 22 are determined to be from blasting works, while 13 remain from an origin that we cannot yet determine. We also find that lightning produces a plentiful supply of natural seismic sources through the conversion of acoustic waves propagating through the atmosphere (thunder), to seismic waves. We record hundreds of thunder quakes with a high signal to noise ratio and over a wide frequency range. We suggest that a tropical region such as Singapore has high potential to further advance thunder-quake studies.