Seismotectonic setting at the North Anatolian Fault Zone after the 1999 Mw=7.4 Izmit earthquake based on high-resolution aftershock locations

International audienceThe most recent devastating earthquakes that occurred along the North Anatolian Fault Zone (NAFZ) in northwestern Turkey were the 1999 Izmit (Mw=7.4) and Düzce (Mw=7.1) events. In this study we present a catalog of Izmit aftershock hypocenters that was deduced from a network covering the entire 140 km long rupture of the mainshock. 7348 events with a location accuracy better than 5 km are analysed. Aftershocks were observed along the entire ruptured segment along a 20 km wide band of activity. Events are clustered in distinct regions and dominantly occur at 5 to 15 km depth. The eastern termination of the Izmit rupture is characterized by a sharp and steeply dipping boundary exactly where the Düzce mainshock initiated 87 days after the Izmit event. Relocation of the events using double-difference technology results in 4696 high-resolution hypocenters that allow resolving the internal structure of the seismically active areas with a resolution of 300 m (horizontal) and 400m (vertical). Below the Akyazi Plain, representing a small pull-apart structure at a triple junction of the NAFZ, we identify planes of activity that can be correlated with nodal planes of EW extensional normal faulting aftershocks. Along the easternmost Karadere-Düzce segment we identify the down-dip extension of the Karadere fault that hosted about 1 m of right-lateral coseismic slip. At the easternmost rupture we correlate a cloud-type distribution of seismic activity with the largest aftershocks in this area, a subevent of the Izmit mainshock and the Düzce mainshock that all have an almost identical focal mechanism. This part of the NAFZ is interpreted as a classical example of a seismic barrier along the fault

Site effect assessment in Bishkek (Kyrgyzstan) using earthquake and noise recording data

Kyrgyzstan, which is located in the collision zone between the Eurasian and Indo-Australian lithosphere plates, is prone to large earthquakes as shown by its historical seismicity. Hence, an increase in the knowledge and awareness by local authorities and decision makers of the possible consequence of a large earthquake, based on improved seismic hazard assessments and realistic earthquake risk scenarios, is mandatory to mitigate the effects of an earthquake. To this regard, the Central Asia Cross-Border Natural Disaster Prevention (CASCADE) project aims to install a cross- border seismological and strong motion network in Central Asia and to support microzonation activities for the capitals of Kyrgyzstan, Uzbekistan, Kazakhstan, Tajikistan, and Turkmenistan. During the first phase of the project, a temporary seismological network of 19 stations was installed in the city of Bishkek, the capital of Kyrgyzstan. Moreover, single-station noise recordings were collected at nearly 200 sites. In this study, the site amplifications occurring in Bishkek are assessed by analyzing 56 earthquakes extracted from the data streams continuously acquired by the network, as well as from the single-station noise measurements. A broadband amplification (starting at ∼0:1 and 0.2 Hz), is shown by the standard spectral ratio (SSR) results of the stations located within the basin. The reliability of the observed low-frequency amplification was validated through a time–frequency analysis of denoised seismograms. Discrepancies between horizontal-to-vertical spectral ratio and SSR results are due to the large amplification of the vertical component of ground motion, probably due to the effect of converted waves. The single-station noise results, once their reliability was assessed by their comparison with the earthquake data, have been used to produce the first fundamental resonance frequency map for Bishkek, whose spatial variation shows a good agreement with the presence of an impedance contrast within the Tertiary sedimentary cover.Published3068-30824.1. Metodologie sismologiche per l'ingegneria sismicaJCR Journalope

Analysis of two human pre-ribosomal factors, bystin and hTsr1, highlights differences in evolution of ribosome biogenesis between yeast and mammals

Recent studies reveal that maturation of the 40S ribosomal subunit precursors in mammals includes an additional step during processing of the internal transcribed spacer 1 (ITS1), when compared with yeast Saccharomyces cerevisiae, even though the protein content of the pre-40S particle appears to be the same. Here, we examine by depletion with siRNA treatment the function of human orthologs of two essential yeast pre-ribosomal factors, hEnp1/bystin and hTsr1. Like their yeast orthologs, bystin is required for efficient cleavage of the ITS1 and further processing of this domain within the pre-40S particles, whereas hTsr1 is necessary for the final maturation steps. However, bystin depletion leads to accumulation of an unusual 18S rRNA precursor, revealing a new step in ITS1 processing that potentially involves an exonuclease. In addition, pre-40S particles lacking hTsr1 are partially retained in the nucleus, whereas depletion of Tsr1p in yeast results in strong cytoplasmic accumulation of pre-40S particles. These data indicate that ITS1 processing in human cells may be more complex than currently envisioned and that coordination between maturation and nuclear export of pre-40S particles has evolved differently in yeast and mammalian cells

Seismic Imaging of the Reykjanes Peninsula, Iceland: Crustal‐Scale Context of Geothermal Areas and Ongoing Volcano‐Tectonic Unrest

Volcanic and seismic unrest on the Reykjanes Peninsula in SW Iceland that started in late 2019 after ∼800 years of quiescence has drawn wide interest to this on‐land extension of the Mid‐Atlantic spreading ridge. Here, we use seismic data collected across the larger Peninsula region, covering six volcanic systems and associated high‐temperature geothermal areas to produce a crustal‐scale shear‐wave velocity model. The model is constructed from receiver functions (RF), and pre‐existing surface wave dispersion measurements from recent studies, supplemented with new inter‐station paths from recent seismic deployments. We compare our velocity model to RF stacks which highlight seismic discontinuity boundaries. Results show local seismicity and geothermal systems are limited to the upper crust, which is split into an upper region of extrusive‐dominated heavily fractured material <3 km and intrusive‐dominated more cohesive material below. The gabbroic lower‐crust is dominated by cumulates beyond 10 km depth, which are particularly high‐velocity west offshore of the Peninsula. Crustal thicknesses increase from 15 to 20 km eastwards, likely reflecting increasing temperature and active‐upwelling toward the center of the Iceland hotspot. Reported magma storage depths, for current and historic eruptions, generally sit within the lower‐crust, but several, including for the 2021 Fagradalsfjall eruption, indicate sub‐Moho storage, sourced from a seismically slow region we observe extending to 25 km, which is interpreted as representing a partially molten crust‐mantle transitional region. Our seismic imaging of the Reykjanes Peninsula crust gives insight into regional crustal structure and tectonic processes, as well as providing large‐scale context for the continuing volcano‐tectonic unrest the region is experiencing