Problems with the interpretation of the 220 nm interstellar feature

The bump in the ultraviolet part of the interstellar extinction curve provides a great challenge in the modelling of interstellar dust. Its shape can be well approximated by a classical dispersion profile with a total halfwidth of 48 nm centred at 217 nm. Apart from few slightly deviating cases the parameters of the band seem to be surprisingly constant in the solar neighbourhood.The equivalent widthW of the 217 nm band shows a very tight correlation with the colour excessE(B-V). Studies of correlations with the strength of diffuse interstellar bands gave no conclusive results as to the nature of the band.The most common interpretation of the 217 nm feature as originating from small graphite grians meets several difficulties. No final decision on the carrier can be made at present.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986.     

Amplitude Response of a LCR Gravimeter with Feedback at Periods of Microseisms and Earthquake Waves

The amplitude response of a LCR gravimeter with the SRW-E feedback was determined on a vertical vibrating platform. The ink-pen recorder was connected parallel with the digital voltmeter input to obtain an analog response of the gravimeter to the harmonic motion of the base with a peak-to-peak amplitude of 10 m and periods excited in an interval of 4 - 10 s as by the ground motion of meteorological microseisms, and in the interval 10 -100 s as by surface waves of distant strong earthquakes. In the first interval, an unexpected maximum of the amplitude response was observed with the double amplitude of apparent 6,5 Gal (6.5 × 10 _–8 m/s ² ) at a period of 4.8 s, and a baseline shift with the amplitude of–64Gal was observed at the same period. The value of this direct component cannot be separated from the effect of the Earth's gravity field. In the second interval, the amplitude response of the gravimeter displayed one expected maximum at a period of 40 s with the double amplitude of 8.1Gal. At the usual level of microseisms with a peak-to-peak amplitude of up to 2 m the fluctuation of the gravimeter on the direct baseline shifted by –4.9 Gal was estimated at 1 Gal. With typical Rayleigh surface waves with periods of 20 s and double amplitudes of up to 100 m, the fluctuation reached 67 Gal.     

A seismic hazard assessment and the results of detailed seismic zoning for urban territories of Sakhalin Island

This work briefly discusses the main features of probabilistic seismic hazard analysis (PSHA). Special attention is paid to the identification and quantification of uncertainties related to seismic source characteristics and seismic engineering models for prediction of strong ground motions. The principal seismic models and the results of PSHA application for detailed seismic zoning of urban territories in Sakhalin Island are presented.     

Source parameters of intermediate-depth Vrancea (Romania) earthquakes from empirical Green's functions modeling

Several source parameters (source dimensions, slip, particle velocity, static and dynamic stress drop) are determined for the moderate-size October 27th, 2004 (M_W = 5.8), and the large August 30th, 1986 (M_W = 7.1) and March 4th, 1977 (M_W = 7.4) Vrancea (Romania) intermediate-depth earthquakes. For this purpose, the empirical Green's functions method of Irikura [e.g. Irikura, K. (1983). Semi-Empirical Estimation of Strong Ground Motions during Large Earthquakes. Bull. Dis. Prev. Res. Inst., Kyoto Univ., 33, Part 2, No. 298, 63–104., Irikura, K. (1986). Prediction of strong acceleration motions using empirical Green's function, in Proceedings of the 7th Japan earthquake engineering symposium, 151–156., Irikura, K. (1999). Techniques for the simulation of strong ground motion and deterministic seismic hazard analysis, in Proceedings of the advanced study course seismotectonic and microzonation techniques in earthquake engineering: integrated training in earthquake risk reduction practices, Kefallinia, 453–554.] is used to generate synthetic time series from recordings of smaller events (with 4 ≤ M_W ≤ 5) in order to estimate several parameters characterizing the so-called strong motion generation area, which is defined as an extended area with homogeneous slip and rise time and, for crustal earthquakes, corresponds to an asperity of about 100 bar stress release [Miyake, H., T. Iwata and K. Irikura (2003). Source characterization for broadband ground-motion simulation: Kinematic heterogeneous source model and strong motion generation area. Bull. Seism. Soc. Am., 93, 2531–2545.] The parameters are obtained by acceleration envelope and displacement waveform inversion for the 2004 and 1986 events and MSK intensity pattern inversion for the 1977 event using a genetic algorithm. The strong motion recordings of the analyzed Vrancea earthquakes as well as the MSK intensity pattern of the 1977 earthquake can be well reproduced using relatively small strong motion generation areas, which corresponds to small asperities with high stress drops (300–1200 bar) and high particle velocities (3–5 m/s). These results imply a very efficient high-frequency radiation, which has to be taken into account for strong ground motion prediction, and indicate that the intermediate-depth Vrancea earthquakes are inherently different from crustal events.     

Damages observed in locations of Oaxaca due to the Tehuantepec Mw8.2 earthquake,Mexico

On September 7, 2017, at 23:49 h (local time), a Mw8.2 intermediate-depth normal-fault earthquake occurred in the Gulf of Tehuantepec, 133 km away from Pijijiapan, Chiapas, and about 700 km away from Mexico City. This event caused 95 fatalities and severe damage to different types of structures located close to the epicenter. The main objective of this work is to present observed damages caused in the state of Oaxaca by this earthquake, which were mainly concentrated in self-built houses and historical and ancient buildings. The locations visited by the reconnaissance team of the Institute of Engineering from UNAM in Oaxaca included Salina Cruz, Tehuantepec, Ixtaltepec, Juchitán, Huatulco and La Ventosa.

     

Global distribution of electron temperature and density fluctuations measured by AEROS-B

Abstract

Between July 1974 and September 1975 aboard AEROS-B the electron temperature and the electron density have been measured by the Retarding Potential Analyses and the Impedance Probe respectively in the altitude range 200–870 km. Temperature and density fluctuations along satellite paths have been analysed by digital filtering. The large amount of data allows the mean fluctuations at different heights and latitude intervals to be evaluated. The resulting two-dimensional arrays are presented for some time periods. The global distributions show different patterns in the polar and equatorial regions, and seasonal variations. Mean temperature fluctuations and fluctuations of electron density in general occur simultaneously though with different amplitudes. At high latitudes a seasonal dependence in the strength of the fluctuations of both quantities was observed.