Systematic Investigation of Dynamic Earthquake Triggering in Japan

<p><strong>Introduction. </strong>Previous studies (e.g., Harrington and Brodsky, 2006) documented a relative scarcity of remote triggering in Japan, compared to other seismic regions. For example, in California, dynamic triggering is reported to occur at levels of stress as small as 0.1 kPa, while in Japan it was reported that levels of 30 kPa or more are required to trigger detectable events (van der Elst and Brodsky, 2010). However, the threshold dynamic triggering level following the 2016 M7.3 Kumamoto earthquake was of just a few kPa (Enescu et al., 2016). Enescu et al. (2016) proposed that one of the possibilities to explain this observation is a change of stress triggering threshold that may have taken place after the 2011 M9.0 Tohoku-Oki earthquake.</p><p><strong>Motivation.</strong> Given the above observations, this study investigates 1) the occurrence of dynamically triggered earthquakes in Japan after some large earthquakes from 2004, and 2) whether the threshold of dynamic triggering may have changed due to the 2011 Tohoku-Oki earthquake and why this threshold might have changed.</p><p><strong>Analysis and Results.</strong> First, we investigated dynamic triggering throughout Japan, following some large earthquakes occurred after 2004. As a result, the  threshold appears to decrease following the 2011 Tohoku-Oki earthquake, however the number of earthquakes we have investigated was relatively small, so we could not draw statistically significant conclusions. In the second part of the study, we have focused on a few specific areas within Japan to systematically investigate dynamic triggering, which reduced significantly the computational costs. Thus, we focused on some areas in Tohoku and Hida, where swarm earthquakes occurred after the 2011 Tohoku-Oki earthquake. As a result, the change of the triggering level in an area close to the Yamagata-Fukushima border is considered to be statically significant at a 5% significance level. In other regions, the significance at a 5% level could not be established, however a decrease of this threshold is apparent, except for one region. We speculate that changes in the stress triggering threshold levels might be related to pore pressure changes in the crust following the 2011 Tohoku-Oki earthquake.</p>

A Shallow Shock: The 25 February 2019 ML 4.9 Earthquake in the Weiyuan Shale Gas Field in Sichuan, China

Earthquakes rarely occur at extremely shallow depths, for example, less than 2 km. Even for induced earthquakes that are typically shallower than tectonic events, only very small ones have been reported in such depths. The ML 4.9 earthquake (Mw 4.3) that struck the Rongxian County, Sichuan, China on 25 February 2019 was an extremely shallow event. Seismological and geodetic data constrained the mainshock depth at ∼1 km with a thrust-faulting mechanism, consistent with the Molin fault orienting northwest. Two foreshocks with magnitudes larger than 4 occurred on an unmapped fault striking northeast, right next to an injection well where hydraulic fracturing (HF) was conducted. The focal depths of the two foreshocks were at ∼2.7 km, coinciding with the depth of HF. Coulomb failure stresses of the two foreshocks on the Molin fault was ∼3 kPa, smaller than typical static triggering threshold (10 kPa), and thus their triggering effects were mild. As the fault was hydraulically sealed from HF, we suggested that the ML 4.9 earthquake was possibly triggered by nearby HF activities through poroelastic stress transfer. Such findings held significant implications for shale gas development by considering seismic hazard associated with shallow faults.

Correction: A flexible, multifunctional, active terahertz modulator with an ultra-low triggering threshold

Correction for ‘A flexible, multifunctional, active terahertz modulator with an ultra-low triggering threshold’ by He Ma et al., J. Mater. Chem. C, 2020, DOI: 10.1039/d0tc02446e.

A flexible, multifunctional, active terahertz modulator with an ultra-low triggering threshold

Flexible, multifunctional, active THz modulators with ultra-low triggering threshold were developed by aligned carbon nanotube thin films coated with VO2. These active THz modulators find applications in THz communication and THz imaging.

Self-Determination in the Context of Personal and Professional Development of an Educator

A humanitarian tendency of education gives greater urgency to person-centered conceptualization, which puts the idea of self-determination in the first place in the view of the making of heuristic ideas about personal and professional development of an educator. The paper aims at conceptualizing motivational processes of self-determination as a triggering threshold of personal and professional development of an educator. Self-determination and related concepts of self-regulation, self-motivation, facilitation, dialogue, productivity, and commitment have been found to determine the essence of personal and professional development of an educator as a psychological resource system. The authors have come to the conclusion that creative content of self-determination processes is due to integrity and effectiveness of personal and professional development of an educator.