Tectonic tremors in the Northern Mexican subduction zone remotely triggered by the 2017 Mw8.2 Tehuantepec earthquake

Surface waves from the 2017 Mw8.2 Tehuantepec earthquake remotely triggered tectonic tremors in the Jalisco region, approximately 1000 km WNW in the northern Mexican subduction zone. This is the first observation of tremor triggering in this region and one of the largest known examples of a triggered tremor in the world. Although prior studies have found tectonic tremors triggered by teleseismic waves in subduction zones and plate boundaries, further investigation of tremor triggering is crucially important for understanding the causative mechanism. We calculate the stress and strain changes across the three-dimensional plate interface attributable to seismic waves from the earthquake by full wavefield simulation. The maximum magnitude of the dynamic strain tensor eigenvalues on the plate interface, where tremors likely occur, is approximately 10–6. The subducting slab geometry effectively amplifies triggering waves. The triggering Coulomb failure stress changes resolved for a thrust fault plane consistent with the geometry are estimated to be approximately 10–40 kPa. The relationship between the triggering stress and triggered tremor amplitude may indicate that the aσ of the rate–state-dependent friction law is 10–100 kPa

Dynamic Earthquake Triggering in Southern California in High Resolution: Intensity, Time Decay, and Regional Variability

遠地地震によって誘発される地震活動の特徴を解明 --地震ビッグデータ解析を通じて--. 京都大学プレスリリース. 2021-05-06.Earthquake triggering by seismic waves has been recognized as a phenomenon for nearly 30 years. However, our ability to study dynamic triggering has been limited by our ability to capture the triggering stresses accurately and record the resultant earthquakes. Here we use full waveforms from a dense seismic network and a modern, high‐resolution seismic catalog to measure triggering in Southern California from 2008 to 2017 based on interevent time ratios. We find that the fractional seismicity rate change, which we term triggering intensity or triggerability, as a function of peak strain change for the period of ∼20 s due to distant earthquakes is monotonically increasing and compatible with earlier measurements made with a disjoint data set from 1984 to 2008. A triggering strain of 1 microstrain is equivalent to the local productivity generated by an M1.8 earthquakes. This result implies that a prediction of seismicity rate changes can be made based on recorded ground shaking using the same formalism as currently used for aftershock prediction. For a teleseismic event, this small level of triggering occurs throughout the region and thus aggregates to a regional effect. We find that the triggering rate decays after the triggerer follows an Omori‐Utsu law, but at a much slower rate than a typical aftershock sequence. The slow decay rate suggests that an ancillary process such as creep or fluid flow must be part of dynamic triggering. The prevalence of triggering in areas of creep or fluid involvement reinforces this inference. A triggering cascade of secondary earthquakes is insufficient to explain the data

Large-scale mapping observations of the CI(3P1-3P0) and CO(J=3-2) lines toward the Orion A molecular cloud

Large scale mapping observations of the 3P1-3P0 fine structure transition of atomic carbon (CI, 492 GHz) and the J=3-2 transition of CO (346 GHz) toward the Orion A molecular cloud have been carried out with the Mt. Fuji submillimeter-wave telescope. The observations cover 9 square degrees, and include the Orion nebula M42 and the L1641 dark cloud complex. The CI emission extends over almost the entire region of the Orion A cloud and is surprisingly similar to that of 13CO(J=1-0).The CO(J=3-2) emission shows a more featureless and extended distribution than CI.The CI/CO(J=3-2) integrated intensity ratio shows a spatial gradient running from the north (0.10) to the south (1.2) of the Orion A cloud, which we interpret as a consequence of the temperature gradient. On the other hand, the CI/13CO(J=1-0) intensity ratio shows no systematic gradient. We have found a good correlation between the CI and 13CO(J=1-0) intensities over the Orion A cloud. This result is discussed on the basis of photodissociation region models.Comment: Text file is 13 pages long, and 3 figure files (pdf format). NRO Report No. 508 (1999). University of Tokyo, Resceu 41/9

DOCK2 is involved in the host genetics and biology of severe COVID-19

「コロナ制圧タスクフォース」COVID-19疾患感受性遺伝子DOCK2の重症化機序を解明 --アジア最大のバイオレポジトリーでCOVID-19の治療標的を発見--. 京都大学プレスリリース. 2022-08-10.Identifying the host genetic factors underlying severe COVID-19 is an emerging challenge. Here we conducted a genome-wide association study (GWAS) involving 2, 393 cases of COVID-19 in a cohort of Japanese individuals collected during the initial waves of the pandemic, with 3, 289 unaffected controls. We identified a variant on chromosome 5 at 5q35 (rs60200309-A), close to the dedicator of cytokinesis 2 gene (DOCK2), which was associated with severe COVID-19 in patients less than 65 years of age. This risk allele was prevalent in East Asian individuals but rare in Europeans, highlighting the value of genome-wide association studies in non-European populations. RNA-sequencing analysis of 473 bulk peripheral blood samples identified decreased expression of DOCK2 associated with the risk allele in these younger patients. DOCK2 expression was suppressed in patients with severe cases of COVID-19. Single-cell RNA-sequencing analysis (n = 61 individuals) identified cell-type-specific downregulation of DOCK2 and a COVID-19-specific decreasing effect of the risk allele on DOCK2 expression in non-classical monocytes. Immunohistochemistry of lung specimens from patients with severe COVID-19 pneumonia showed suppressed DOCK2 expression. Moreover, inhibition of DOCK2 function with CPYPP increased the severity of pneumonia in a Syrian hamster model of SARS-CoV-2 infection, characterized by weight loss, lung oedema, enhanced viral loads, impaired macrophage recruitment and dysregulated type I interferon responses. We conclude that DOCK2 has an important role in the host immune response to SARS-CoV-2 infection and the development of severe COVID-19, and could be further explored as a potential biomarker and/or therapeutic target

The whole blood transcriptional regulation landscape in 465 COVID-19 infected samples from Japan COVID-19 Task Force

「コロナ制圧タスクフォース」COVID-19患者由来の血液細胞における遺伝子発現の網羅的解析 --重症度に応じた遺伝子発現の変化には、ヒトゲノム配列の個人差が影響する--. 京都大学プレスリリース. 2022-08-23.Coronavirus disease 2019 (COVID-19) is a recently-emerged infectious disease that has caused millions of deaths, where comprehensive understanding of disease mechanisms is still unestablished. In particular, studies of gene expression dynamics and regulation landscape in COVID-19 infected individuals are limited. Here, we report on a thorough analysis of whole blood RNA-seq data from 465 genotyped samples from the Japan COVID-19 Task Force, including 359 severe and 106 non-severe COVID-19 cases. We discover 1169 putative causal expression quantitative trait loci (eQTLs) including 34 possible colocalizations with biobank fine-mapping results of hematopoietic traits in a Japanese population, 1549 putative causal splice QTLs (sQTLs; e.g. two independent sQTLs at TOR1AIP1), as well as biologically interpretable trans-eQTL examples (e.g., REST and STING1), all fine-mapped at single variant resolution. We perform differential gene expression analysis to elucidate 198 genes with increased expression in severe COVID-19 cases and enriched for innate immune-related functions. Finally, we evaluate the limited but non-zero effect of COVID-19 phenotype on eQTL discovery, and highlight the presence of COVID-19 severity-interaction eQTLs (ieQTLs; e.g., CLEC4C and MYBL2). Our study provides a comprehensive catalog of whole blood regulatory variants in Japanese, as well as a reference for transcriptional landscapes in response to COVID-19 infection

Propagation of an earthquake triggering front from the 2011 Tohoku-Oki earthquake

Increases in seismicity have been widely observed at varying distances from the source area following large earthquakes. The increased number of earthquakes are usually called aftershocks if the area is within a rupture length of the mainshock, and called remotely triggered events if they are well beyond that distance. These earthquakes can be explained as being induced by static and/or dynamic stress changes due to the mainshock. However, clear observations of dynamic triggering have been inadequate to differentiate between the two mechanisms. This study shows that early post-seismic events triggered by the 2011 M(w) 9.0 Tohoku-Oki earthquake systematically propagated over Japan in a southwestern direction, associated with the strong seismic waves from the source. The propagation front was consistent with the arrivals of large amplitude surface waves traveling at 3.1 to 3.3 km/s and extending to a distance of 1, 350 km. There were no observations of triggered earthquakes in the northern direction. Dynamic stress changes toward the north were comparable to or smaller than those necessary for triggering in the southwestern direction. Static stress changes were one to two orders smaller than dynamic stress changes at remote distance, indicating that static stress was not the main mechanism of the triggering. Furthermore, the dynamic stress/strain changes play an important role for remote triggering if the value is more than ∼500 kPa in stress or ∼10[−6] in strain

Bayesian approach for detecting dynamically triggered very low-frequency earthquakes in the Nankai subduction zone and application to the 2016 Mw5.9 off-Kii Peninsula earthquake, Japan

A correction has been published: Geophysical Journal International, Volume 218, Issue 2, August 2019, Page 977, https://doi.org/10.1093/gji/ggz218.Remote triggering of very low-frequency (VLF) earthquakes in the Nankai subduction zone by surface waves from a moderate to large, distant earthquake was examined using a Bayesian approach. The triggering of another type of tectonic slow earthquake/tremor and slow slip was previously discovered using simple signal processing techniques that exploit the different characteristic periods of the triggered and triggering event waveforms. Meanwhile, detecting low-amplitude VLF earthquakes embedded in high-amplitude seismic waves is challenging when they have similar characteristic periods, as established detection algorithms are inapplicable in such cases. Here we use a particle filter/smoother for time-series analysis combined with Markov chain Monte Carlo methods, to detect seismic signals and estimate the maximum likelihood source parameters of VLF events that might have been remotely triggered by surface waves from a moderate to large, distant earthquake, in data where the surface waves and target signals both have predominant periods between 10 and 100 s. This approach was applied to seismograms of the 2016 Mw 5.9 off-Kii Peninsula earthquake (Japan), recorded by the KiK-net borehole array in western Shikoku, Japan, where VLF events were previously reported. The borehole array is used because comparing surface and borehole records can identify vertically incident body waves based on depth-dependent phase differences, which do not appear in records of horizontally propagating surface waves. In particle filtering/smoothing, waveforms of a probable VLF event at each seismic station are predicted by a full-wavefield simulation in a 3-D structure model, and seismic interferometry that estimates traveltimes between surface and borehole sensors. A maximum-likelihood approach is used to estimate source parameters that best explain the surface observations predicted by the borehole observations and probable VLF signals. We found that six VLF events with magnitudes 3.4 ≤ Mw ≤ 4.3 likely occurred in the seismogenic regions of ambient low-frequency earthquakes/tremors (LFEs), and were likely triggered by the arrivals of high-amplitude surface waves. The triggering stress changes are estimated from 0.4 to 1.5 kPa, similar to the values for triggered LFEs reported previously. Since there were no triggered LFEs in western Shikoku following the 2016 Mw 5.9 earthquake, these VLF earthquakes are more sensitive to stress changes caused by surface waves from large earthquakes. This is the first reported example of dynamic triggering of VLF earthquakes