Understanding the 6 February 2018, Hualien earthquake sequence through catalog compilation

Abstract

In this study, we compiled the Central Weather Bureau (CWB) data in order to study the Gutenberg-Richter magnitude-frequency slopes (i.e., b-values) and seismicity rates of significant earthquake sequences in the area of Hualien. A total of ten events between 1973 and 2018 were selected for analysis. Using time windows 72 h before and after the main shock, we first examined the existence of detectable foreshocks and then applied the Gutenberg-Richter law and Omori's law to determine the b-value and seismicity rate, respectively. The compiled results were used to assess the abnormalities and other characteristics of the 2018 Hualien earthquake for their forecast potential. We concluded that seismicity rates alone are not sufficient to forecast whether a greater main shock is forthcoming. The foreshock sequence of the 2018 Hualien earthquake was characterized by a low b-value and a high seismicity rate. Another earthquake with a prominent foreshock sequence occurred in 1990, but it showed a different relationship between the magnitude and the seismicity rate. For both the 1990 and the 2018 Hualien earthquakes, we found that the b-values of the foreshocks were lower than those of the respective aftershocks. The b-values for earthquake sequences are depressed relative to the background seismicity in the area. The mechanisms proposed for temporal variation in b-values are briefly reviewed to explain the observed b-value patterns. Finally, we established an empirical relationship with moment magnitude (M w ) in order to estimate the spatial range of aftershock distributions in the area of Hualien for shallow earthquakes (hypocenter depth ≤ 20 km) with M w ≥ 5.3.

Introduction to the special issue on the 2018 Hualien, Taiwan, earthquake

“…It not only shows the improvements on short-term hazard evaluation but also independently supports the multi-sequence nature of the 2018 Hualien earthquake. This study also confirmed the low bvalue obtained in 72 hr after Hualien main shock in Chen et al (2019c). Chen et al (2019b) demonstrates the efficiency of the CWB Early Warning System on the 2018 Hualien earthquake sequence.…”

“…Two studies concern the seismicity rate of the Hualien sequences that are related to the hazard potential. Chen et al (2019c) explored the temporal evolution of the 2018 Hualien earthquake sequence and other major events previous occurred in the nearby region based on the CWB seismicity catalogues. For both foreshocks and aftershocks of the 2018 Haulien sequence, the seismicity rates (K-values) are relatively high among all 11 studied events, while the b-values are almost the lowest (0.63 and 0.68), which is also significantly below the long term background average (0.99).…”

Evaluation of aftershock hazard of the 2018 M 6.2 Hualien earthquake

“…The M L 6.2 earthquake with epicentre (24.10°N, 121.73°E) and hypocentre at depth 10.6 km occurred at 2350 LT, 6 February 2018 near Hualien, Taiwan (Chen et al 2019). To have a reliable analysis of the aftershock hazard after the Hualien shock, we employ the earthquake catalogue published by the Central Weather Bureau (CWB) at http://gdms.cwb.gov.tw/index.php.…”

Triggered slip on multifaults after the 2018 Mw 6.4 Hualien earthquake by continuous GPS and InSAR measurements

“…Thousands of aftershocks were recorded by Geophysical Database Management System (https://gdms.cwb.gov.tw/ index.php) of CWB within 14 days . Aftershocks were propagated southward from the hypocenter of the mainshock to the Longitudinal Valley Chen et al 2019).…”