Frequency Distribution Of Events Research Articles

Evaluation of Flood and Landslide Risk to the Population of Italy

We have compiled a database of floods and landslides that occurred in Italy between AD 1279 and 2002 and caused deaths, missing persons, injuries, and homelessness. Analysis of the database indicates that more than 50,593 people died, went missing, or were injured in 2580 flood and landslide events. Harmful events were inventoried in 26.3% of the 8103 Italian municipalities. Fatal events were most frequent in the Alpine regions of northern Italy and were caused by both floods and landslides. In southern Italy, landslides were the principal agents of fatalities and were most numerous in the Campania region. Casualties were most frequent in the autumn. Fast-moving landslides, including rock falls, rockslides, rock avalanches, and debris flows, caused the largest number of deaths. In order to assess the overall risk posed by these processes, we merged the historical catalogs and identified 2682 "hydrogeomorphological" events that triggered single or multiple landslides and floods. We estimated individual risk through the calculation of mortality rates for both floods and landslides and compared these rates to the death rates for other natural, medical, and human-induced hazards in Italy. We used the frequency distribution of events with fatalities to ascertain the magnitude and frequency of the societal risks posed by floods and landslides. We quantified these risks in a Bayesian model that describes the probabilities of fatal flood and landslide events in Italy.

Hard X‐Ray and Microwave Observations of Microflares

In this paper, we study solar microflares using the coordinated hard X-ray and microwave observations obtained by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) during its open-shutter operation mode and the Owens Valley Solar Array (OVSA). The events in our study are selected in the energy range of 12-25 keV and are relatively large microflares with an average GOES soft X-ray incremental flux at the B2.0 level. A total of 760 microflares are identified from the RHESSI burst catalog. Of the 200 microflares that fall into the OVSA observing window, about 40% are detected in microwaves. Using these hundreds of events as samples, we study the event distribution with respect to the flux, the solar activity, and active regions, in comparison with flares of larger scales. Nonthermal properties of microflares are investigated through spectral analysis of X-rays and microwaves. (1) We find that the event frequency distribution with respect to the RHESSI peak count rates at 12-25 keV can be accurately described with a power-law function down to 8 counts s-1, the power-law index being 1.75 ± 0.03, consistent with previous studies. (2) Similar to large flares, the occurrence rate of microflares is correlated with solar activity. The studied samples of microflares are mostly produced by active regions, as suggested by the large percentage of events detected by OVSA, which observes target active regions. However, all active regions do not have equal productivity, and certain active regions are a lot more productive than other regions. (3) While some large and complex active regions are predominantly productive in both very weak and strong events, we also find an active region that produces many microflares and C-class events but does not produce powerful events. (4) Analysis of energy-dependent time profiles suggests that there is a pronounced temporal correlation between the time derivative of soft X-rays and 14-20 keV hard X-rays, i.e., the Neupert effect, in about one-half the studied events. (5) Albeit small, many microflares exhibit hard X-ray emission at over 10 keV and microwave emission at around 10 GHz. Spectral analysis in these two wavelengths corroborates the nonthermal nature of these emissions. (6) In a limited number of samples, the RHESSI spectral fitting yields a photon spectral index of 4.5-7, and microwave spectral analysis on the same events shows that the power-law index of the electron spectrum is in the range of 2-5. The discrepancy in the electron spectrum index derived from hard X-rays and microwaves is substantially greater than previously reported in big flares, hinting at the existence of high-energy, microwave-emitting electrons that have a much hardened spectrum compared with electrons emitting hard X-rays.

Learning decision trees from decision rules: A method and initial results from a comparative study

A standard approach to determining decision trees is to learn them from examples. A disadvantage of this approach is that once a decision tree is learned, it is difficult to modify it to suit different decision making situations. Such problems arise, for example, when an attribute assigned to some node cannot be measured, or there is a significant change in the costs of measuring attributes or in the frequency distribution of events from different decision classes. An attractive approach to resolving this problem is to learn and store knowledge in the form of decision rules, and to generate from them, whenever needed, a decision tree that is most suitable in a given situation. An additional advantage of such an approach is that it facilitates buildingcompact decision trees, which can be much simpler than the logically equivalent conventional decision trees (by compact trees are meant decision trees that may contain branches assigned aset of values, and nodes assignedderived attributes, i.e., attributes that are logical or mathematical functions of the original ones). The paper describes an efficient method, AQDT-1, that takes decision rules generated by an AQ-type learning system (AQ15 or AQ17), and builds from them a decision tree optimizing a given optimality criterion. The method can work in two modes: thestandard mode, which produces conventional decision trees, andcompact mode, which produces compact decision trees. The preliminary experiments with AQDT-1 have shown that the decision trees generated by it from decision rules (conventional and compact) have outperformed those generated from examples by the well-known C4.5 program both in terms of their simplicity and their predictive accuracy.

The El Asnam (Algeria) earthquake of 10 October 1980; conclusions drawn from a field study

The El Asnam earthquake (M LH = 7.2; M LV = 7.3; M PV = 6.5) occurred at 12:24:24 G.M.T. on 10 October 1980 in the central part of the Chelif valley in Algeria affecting a rather densely populated region of about 900 000 within 7000 km 2 . (Ambraseys 1980). It destroyed at least 25 000 housing units and rendered 300 000 people homeless. The main shock, which killed about 2500 and injured more than 7000 people, was felt as far away as Spain 550 km distant. It was followed by a damaging aftershock 3 hr later (M LV = 6.1; M PV = 5.9). No foreshocks were recorded, but other phenomena have been reported which could have been premonitory (Fig. 1a). The El Asnam earthquake is the largest event in the Atlas since 1790, and in the Chelif valley since 1716. For the Atlas as a whole, the moment rate calculated from long-term observations is only 10 25 dyn-cm/year. This corresponds to a slip rate of only 0.7 mm/year which is a small fraction of the value calculated from plate motions, implying that much of the deformation of the Atlas occurs aseismically and that the tectonic activity of the region is not fully reflected by its short-term seismicity. This is a serious handicap in the assessment of the earthquake hazard in the Atlas. The frequency distribution of events above magnitude 4 3/4 was found to be f(M) = 2.2 exp(-2.2 M ), with a probable cut-off at about M = 7 1/4 to which corresponds a return period

On the Statistical Nature of Type I Bursts

During noise storms narrow-band, short-lived bursts make up an important part of the activity. Frequently the bursts show different characteristic arrangements in the frequency-time plane (Elgaröy, 1977). In the present investigation the frequency of occurrence of single bursts and sequences of bursts has been determined. The work started out as a search for statistical evidence for the occurrence of echoes of type I bursts. As progress was made, more attention was devoted to the general question of what was the frequency distribution of events containing different numbers of bursts and the conclusions that could be drawn from the observed distribution.

Erratum: Cosmic Flare Transients: Constraints upon Models for Energy Storage and Release Derived from the Event Frequency Distribution

Erratum: Cosmic Flare Transients: Constraints upon Models for Energy Storage and Release Derived from the Event Frequency Distribution

Cosmic flare transients - Constraints upon models for energy storage and release derived from the event frequency distribution

Cosmic flare transients - Constraints upon models for energy storage and release derived from the event frequency distribution