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Vrancea intermediate-depth focal mechanism catalog: a useful instrument for local and regional stress field estimation

Andreea Craiu, Marius Craiu, Marius Mihai, Florinela Manea Elena, Alexandru Marmureanu

Acta Geophysica

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2023

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Vol. 71, no. 1

29--52

EN

The Vrancea seismic zone, located in the bend region of the South-Eastern Carpathians, is a unique area with both crustal and intermediate-depth seismic activity and is known as one of the most active seismic area in Europe. Moderate crustal seismicity is recorded all over the Carpathian region, but the far more intense activity occurs in a small subcrustal seismogenic volume beneath the SE‐bend of the Carpathian arc with about 20×50 km lateral and 110 km vertical extent (70–180 km depth). A unique slab geometry, likely preserved until the present, causes stress localization due to the slab bending and subsequent stress release resulting in large mantle earthquakes in the region. The main focus of this study is to determine the focal mechanisms for events with a magnitude larger than 2.7, between 2005 and 2020 and evaluate the current stress field along the Vrancea subcrustal region, from the derived fault plane solutions. The main style of faulting for Vrancea subcrustal events presents a predominant reverse one, with two main earthquakes categories: the first one with the nodal planes, oriented NE–SW parallel with the Carpathian Arc and the second one with the nodal planes, oriented NW–SE perpendicular on the Carpathian Arc. The results of stress inversion indicate a dominant thrust faulting style, with an average stress regime index of 2.87. The stress pattern shows similar partitioning with vertical extension in the slab and no preferred orientation in the overlying crust, showing a transition regime from the extensional regime in the Moesian Platform to the compressional regime in the Vrancea subcrustal zone.

2

The Optical Gravitational Lensing Experiment. Catalog of Microlensing Events in the Galactic Bulge

Udalski A., Żebruń K., Szymański M., Kubiak M., Pietrzyński G., Soszyński I., Woźniak P.

Acta Astronomica

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2000

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Vol. 50, No. 1

1--65

EN

We present the Catalog of microlensing events detected toward the Galactic bulge in three observing seasons, 1997-1999, during the OGLE-II microlensing survey. The search for microlensing events was performed using a database of about 4×109 photometric measurements of about 20.5 million stars from the Galactic bulge. The Catalog comprises 214 microlensing events found in the fields covering about 11 square degrees on the sky and distributed in different parts of the Galactic bulge. The sample includes 20 binary microlensing events, 14 of them are caustic crossing. In one case a double star is likely lensed. We present distribution of the basic parameters of microlensing events and show preliminary rate of microlensing in different regions of the Galactic bulge. The latter reveals clear dependence on the Galactic coordinates. The dependence on l indicates that the majority of lenses toward the Galactic bulge are located in the Galactic bar. Models of the Galactic bar seem to reasonably predict the observed spatial distribution of microlensing events in the Galactic bulge. All data presented in the Catalog and photometry of all events are available from the OGLE Internet archive.

3

The All Sky Automated Survey. Catalog of about 3800 Variable Stars

Pojmański G.

Acta Astronomica

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2000

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Vol. 50, No. 2

177--190

EN

Results of the first two years of observations using the All Sky Automated Survey prototype camera are presented. More than 140 000 stars in 50 Selected Fields covering 300 square degrees were monitored each clear night in the I-band resulting in the ASAS Photometric I-band Catalog containing over 5×107 individual measurements. Nightly monitoring of over 100 standard stars confirms that most of our data remains within σI=0.03 mag of the standard I system. Search for the stars varying on the time scales longer than a day revealed about 3800 variable stars (mostly irregular, pulsating and binaries) brighter than 13 mag. Only 630 of them are known or suspected variables included in the GCVS (Kholopov 1985). Among the stars brighter than I≈7.5 (which are saturated on our frames) we have found about 50 variables (12 are in the GCVS, 6 others in the Hipparcos catalog. Because of the large volume of data we present here only selected tables and light curves, but the complete ASAS Catalog of Variable Stars (currently divided into Periodic and Miscellaneous sections) and all photometric data are available on the Internet http://www.astrouw.edu.pl/~gp/asas/asas.html or http://archive.princeton.edu/~asas/