Magnitude −7 level earthquakes: A new lower limit of self-similarity in seismic scaling relationships

Microfractures occurring in a rock sample that are called acoustic emission (AE) events show some similar features to earthquakes. However, it remains to be shown whether or not AE equate to ultramicroearthquakes. In this study, we show the existence of magnitude −7 level earthquakes based on seismological analyses of AE source parameters. Advances in multichannel, broadband, high‐speed continuous recording of AE under seismogenic pressure...