![]() In the present work, we present a dynamic rupture source model for very low-frequency earthquake signals. Reconciling this observation and its implications is critically important to better understand the broad spectrum of fault behaviors corresponding to slow earthquakes. This observation suggests that very low-frequency earthquakes do not necessary share the same source mechanism with other types of slow earthquakes, although they may be driven by a similar process. ![]() However, very low-frequency earthquakes have been recently found in the absence of associated tremors and low-frequency earthquakes (Hutchison & Ghosh, 2016, 2019). These observations possibly suggest that signals from different types of slow earthquakes may come from the same underlying source processes. In many cases, very low-frequency earthquakes are found to be accompanied by other types of slow earthquakes such as slow slip events, nonvolcanic or tectonic tremors (referred to as tremors), and low-frequency earthquakes (e.g., Ghosh et al., 2015 Gomberg et al., 2016 Nakano et al., 2018). While very low-frequency earthquake signal can be quite clear on seismograms, the physical source mechanism is not. Therefore, very low-frequency earthquakes are considered as one type of a broader class of slow earthquakes, whose source processes are thought to be slower than regular earthquakes (Obara & Kato, 2016). Very low-frequency earthquakes are observed to have double couple focal mechanisms (e.g., Ghosh et al., 2015 Ide & Yabe, 2014) However, they cannot be typical stick-slip shear slip like regular fast earthquakes, since their source duration is longer than regular earthquakes of similar magnitude (Gomberg et al., 2016 Ito & Obara, 2006). Very low-frequency earthquakes are widely observed in subduction zones around the world, including the southwest Japan subduction zone (e.g., Baba et al., 2018 Ito & Obara, 2006 Nakano et al., 2018), the Ryuku subduction zone (e.g., Ando et al., 2012 Nakamura & Sunagawa, 2015), the Costa Rica subduction zone (e.g., Walter et al., 2013), and the Cascadia subduction zone (e.g., Ghosh et al., 2015 Hutchison & Ghosh, 2016, 2019 Ide, 2016). They are depleted in higher frequencies compared to regular fast local earthquakes of similar magnitude, which typically can be observed in a wide spectrum of ground motion record up to few tens of hertz. Very low-frequency earthquakes, sometimes referred to as very low-frequency events, are seismic events that are observed only in very low-frequency ground motion records-usually between 0.02 and 0.05 Hz. ![]() Our finding contributes to a better understanding of the relationship between different types of slow seismic events and broad spectrum of fault behaviors. ![]() Our result suggests that very low-frequency earthquake could have a different source from other slow earthquakes, such as tremor. In this study, we set up a model for very low-frequency earthquake. It is still not clear whether different types of slow earthquakes share the same source processes. Very low-frequency earthquake is one of them. So far, different types of slow earthquakes are identified. These seismic events are called slow earthquakes. They are results of slow, transient movement along the fault, where the plates do not move as fast as in regular earthquakes. Currently, a number of anomalous seismic events are observed at the edge of seismogenic zone. Outside this seismogenic zone, tectonic plates are thought to be moving past each other slowly, continuously, and silently, in a manner known as creep. Earthquakes are generated wherever faults accommodate their relative motion in a stick-slip manner.
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