Many large earthquakes are preceded by one or more foreshocks, but it is unclear how these foreshocks relate to the nucleation process of the mainshock. On the basis of an earthquake catalog created using a waveform correlation technique, we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude (M(w)) 9.0 Tohoku-Oki earthquake in Japan. The time history of quasi-static slip along the plate interface, based on small repeating earthquakes that were part of the migrating seismicity, suggests that two sequences involved slow-slip transients propagating toward the initial rupture point. The second sequence, which involved large slip rates, may have caused substantial stress loading, prompting the unstable dynamic rupture of the mainshock.

To obtain a precise record of the foreshock sequence before the 2014 Iquique, Chile M w 8.1 earthquake, we applied a matched filter technique to continuous seismograms recorded near the source region. We newly detected about 10 times the number of seismic events listed in the routinely constructed earthquake catalog and identified multiple sequences of earthquake migrations at speeds of 2-10 km/d, both along strike and downdip on the fault plane, updip of the main shock area. In addition, we found out repeating earthquakes from the newly detected events, likely indicating aseismic slip along the plate boundary fault during the foreshock sequence. These observations suggest the occurrence of multiple slow-slip events updip of the main shock area. The final slow-slip event migrated toward the main shock nucleation point. We interpret that several parts of the plate boundary fault perhaps experienced slow slip, causing stress loading on the prospective largest slip patch of the main shock rupture.

The earthquake nucleation process has been vigorously investigated based on geophysical observations, laboratory experiments, and theoretical studies; however, a general consensus has yet to be achieved. Here, we studied nucleation process for the 2014 Iquique, Chile Mw 8.2 megathrust earthquake located within the current North Chile seismic gap, by analyzing a long-term earthquake catalog constructed from a cross-correlation detector using continuous seismic data. Accelerations in seismicity, the amount of aseismic slip inferred from repeating earthquakes, and the background seismicity, accompanied by an increasing frequency of earthquake migrations, started around 270 days before the mainshock at locations up-dip of the largest coseismic slip patch. These signals indicate that repetitive sequences of fast and slow slip took place on the plate interface at a transition zone between fully locked and creeping portions. We interpret that these different sliding modes interacted with each other and promoted accelerated unlocking of the plate interface during the nucleation phase.

The objective of this study was to investigate the effect of long-term melatonin administration on plasma levels of triglycerides, insulin and leptin, and on the fatty-acid metabolism of plasma and hepatic lipids in type 2 diabetic rats. Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an animal model of type 2 diabetes mellitus, were divided into two groups: one untreated (n=6), and one implanted with time-releasing melatonin pellets (1.1 mg/day for 30 wk) under the abdominal skin (n=6). Age-matched Long-Evans Tokushima Otsuka (LETO) rats (n=6) were used as healthy controls. The untreated diabetic rats had the increased plasma levels of triglycerides, cholesterol, insulin and leptin at 35 wk, as compared with the healthy control rats (n=6). The diabetic rats also had augmented ratios of 20:3n-6/20:4n-6 fatty acids, owing to diminished activity of Delta-5 desaturase, an insulin-permissive enzyme, in the liver. Melatonin administration to OLETF rats reduced the hypertriglyceridemia (-39%, P < 0.05), hyperinsulinemia (-33%, P < 0.01) and hyperleptinemia (-43%, P < 0.01), and restored hepatic Delta-5 desaturase activity (148%, P < 0.005). This resulted in a return to normal ratios of 20:3n-6/20:4n-6 fatty acids in plasma and hepatic lipids. There was a significant correlation (r=0.64, P < 0.005) between plasma levels of insulin and the ratios of 20:3n-6/20:4n-6 in plasma phospholipids of all rats in the three groups. Thus, subcutaneous implantation of a melatonin-releasing pellet thus resulted in improved lipid metabolism in diabetic rats, probably through restored insulin resistance.

We explored the detection capability of low-magnitude earthquakes before the 6 April 2009 M w 6.3 L'Aquila event by using a matched filter technique and 512 foreshocks as templates. We analyzed continuous waveforms from 10 broadband seismic stations in a 60 km radius from the epicenter and for 3 months before the main shock. More than 3000 new events, mostly located on the main shock fault, were detected to define the spatial-temporal evolution of micro-seismicity. The foreshock sequence was active northwest of the M w 6.3 hypocenter in January, then migrated toward it at a speed of~0.5 km/day in middle of February. At that time, in a~4 km 2 patch close to the main shock nucleation point, the cumulative number of earthquakes gradually increased until the M w 6.3 event. This patch, characterized by a low b-value, played a key role in controlling the preparation stage to the 2009 L'Aquila main rupture.

A single topical application of 1 jag of 12–O-tetradecanoylphorbol-13-acetate (TPA) to the ears of mice was shown to induce edema, and this TPA-induced inflammation was inhibited by 4-methylsterol and triterpene derivatives. The ED₅₀ of these compounds against TPA-induced inflammation was 0.1–3 μmol. Phytosterols had only slight inhibitory effects. Furthermore, application of 5 μg TPA to mouse skin rapidly caused accumulation of ornithine decarboxylase (ODC). Similarly, sitosterol and lupane-type triterpene derivatives markedly inhibited this TPA-induced ODC accumulation. In addition, 5 umol betulinic acid markedly inhibited the promoting effect of 2.5 μg TPA applied twice weekly on skin tumor formation in mice initiated with 50 ug of 7,12-dimethylbenz[a]anthracene, and 5 μmol of sitosterol caused slight suppression. Thus, the inhibitory effects of sterol and triterpene derivatives on TPA-induced inflammation roughly parallelled their inhibitory activities against tumor promotion.

We investigated the spatiotemporal evolution of an earthquake sequence following a series of large shallow intraplate earthquakes, including a Mw 6.2 foreshock and Mw 7.0 main shock, in the Kumamoto area of Kyushu, SW Japan. To more precisely characterize the evolution of the earthquake sequences, we applied a matched filter technique to continuous waveform data, using template events obtained via a double‐difference relocation algorithm. Migrations of seismicity fronts along the directions of fault strike and dip are clearly seen, starting immediately after the Mw 6.2 foreshock. These migrations are interpreted to result from aseismic slip triggered by the foreshock, propagating toward the nucleation point of the subsequent Mw 7.0 main shock rupture. When combined with static stress changes induced by the Mw 6.2 foreshock, it is likely that stress transfer from both aseismic and seismic slip during the foreshock sequence loaded stress onto the main shock rupture faults, bringing them closer to failure.

Strong ground motion can induce dynamic strains large enough for the Earth's subsurface to respond nonlinearly and to cause permanent, or plastic, damage. The 2011 Mw 9.0 Tohoku‐Oki earthquake, Japan, generated exceptional and well‐recorded ground motions in the greater Tokyo area. We use continuous records from 234 stations of the dense MeSO‐net seismic network to monitor the temporal evolution of the material properties of the shallow subsurface (upper ∼100 m). We apply the single‐station cross‐correlation method to reconstruct the near‐surface reflectivity response through time. We find that the strong ground motions from the mainshock caused large perturbations in the near‐surface structure, with significant drops in seismic velocities up to 11%. For most sites, we observe a logarithmic and complete recovery of the seismic wave speed, suggesting a relaxation process that can be explained by a viscoelastic rheology. Some sites exhibit an instantaneous and permanent change, which suggests a plastic rheology. Finally, dense seismic measurements allow for statistical inference between seismic velocity drops, recovery time scales, and permanent perturbations and ground motion strength and site conditions. This study highlights the potential for seismic interferometry to assess near‐surface rheology with dense seismic arrays.