Hypocenter Hotspots Illuminated Using a New Cross‐Correlation‐Based Hypocenter and Centroid Relocation Method

Abstract

Accurate earthquake locations are important for understanding earthquake processes. Recent advances in earthquake relocation methods have resulted in relative centroid locations with smaller uncertainties using cross‐correlation‐based methods. However, relative hypocenter locations, which are traditionally determined using the onset times of event waveforms, generally possess larger uncertainties than that of the centroids. Here, we develop a new cross‐correlation‐based relative hypocenter relocation method based on the network correlation coefficient method, whereby we incorporate an additional step to search for a suitable window to cross‐correlate the event waveform onsets. We then perform a joint inversion on the obtained relative hypocenter and centroid locations to directly compare their relative locations under a unified coordinate. We apply this method to three regions where repeating earthquakes have been detected, and reveal both the repetitive rupture of similar centroids by these repeating events and newly illuminated hypocenter hotspots that serve as the onset region of earthquakes that grow into different but selective magnitudes. Our joint analysis of hypocenter and centroid locations enables quick estimations of rupture propagation directions without the need to perform slip inversion analyses. We estimate the location uncertainties via bootstrapping, with the 95% confidence intervals yielding sub‐100 m horizontal uncertainties in both the centroid and hypocenter locations with the best station coverage and event availability. These results point to limited but existing correspondence between the hypocenter and centroid locations and the earthquake magnitudes, as well as complexity in the hypocenter distributions, even within repeating earthquake sequences whose rupture areas largely overlap.

The 2021 Mw7.0 and Mw6.7 Miyagi‐Oki Earthquakes Nucleated in a Deep Seismic/Aseismic Transition Zone: Possible Effects of Transient Instability Due To the 2011 Tohoku Earthquake

“…In the Mw5-6 quasi-repeating earthquake source regions, M2-3 repeating earthquakes also occurred (Figures 6a and 6b), forming a hierarchical structure. M2-3 repeating earthquakes occurred inside the source regions of the Mw5-6 repeating earthquakes near the hypocenter of the March Mw7.0 event (Figure 6), showing that seismic patches in this region form a hierarchical structure like that formed by the Kamaishi repeating earthquakes and others (Chang & Ide, 2021;Ide, 2019;Okuda & Ide, 2018;Uchida et al, 2007).…”

A review on slow earthquakes in the Japan Trench

“…Seafloor topography is from Smith and Sandwell (1997). The plate motion is based on Bird (2003) Nishikawa et al Progress in Earth and Planetary Science (2023) 10:1 investigated in detail (e.g., Okada et al 2003;Uchida et al 2007;Okuda and Ide 2018;Ide 2019a;Chang and Ide 2021).…”

Partial Ruptures Cannot Explain the Long Recurrence Intervals of Repeating Earthquakes

“…The small amount of slip accommodated by partial ruptures is observed in Parkfield and potentially in other areas with repeating earthquakes. Chang and Ide (2021) studied three repeating patches in Japan that experienced hierarchical ruptures, which we refer to as partial ruptures. The moment in the reported smaller magnitude events that are observed is only 1%–23% of the total sequence moment, which aligns with what we have observed in Parkfield.…”

“…Such inter‐repeater slip seems plausible—recent studies have observed “hierarchical rupture distributions” of repeating earthquakes in Japan, whereby the ruptures of small earthquakes are located within the rupture areas of larger repeating events (Chang & Ide, 2021; Ide, 2019; Okuda & Ide, 2018; Uchida et al., 2007). If the ruptures of a given patch followed a Gutenberg‐Richter distribution that extended to a maximum magnitude equal to the repeater magnitude, each magnitude 3 repeater should be accompanied by 10–20 observable partial ruptures.…”