76 research outputs found
Archaeoseismology: Methodological issues and procedure
Archaeoseismic research contributes important data on past earthquakes. A limitation of the usefulness of archaeoseismology is due to the lack of continuous discussion about the methodology. The methodological issues are particularly important because archaeoseismological investigations of past earthquakes make use of a large variety of methods. Typical in situ investigations include: (1) reconstruction of the local archaeological stratigraphy aimed at defining the correct position and chronology of a destruction layer, presumably related to an earthquake; (2) analysis of the deformations potentially due to seismic shaking or secondary earthquake effects, detectable on walls; (3) analysis of the depositional characteristics of the collapsed material; (4) investigations of the local geology and geomorphology to define possible natural cause(s) of the destruction; (5) investigations of the local factors affecting the ground motion amplifications; and (6) estimation of the dynamic excitation, which affected the site under investigation. Subsequently, a 'territorial' approach testing evidence of synchronous destruction in a certain region may delineate the extent of the area struck by the earthquake. The most reliable results of an archaeoseismological investigation are obtained by application of modern geoarchaeological practice (archaeological stratigraphy plus geologicalâgeomorphological data), with the addition of a geophysical-engineering quantitative approach and (if available) historical information. This gives a basic dataset necessary to perform quantitative analyses which, in turn, corroborate the archaeoseismic hypothesis. Since archaeoseismological investigations can reveal the possible natural causes of destruction at a site, they contribute to the wider field of environmental archaeology, that seeks to define the history of the relationship between humans and the environment. Finally, through the improvement of the knowledge on the past seismicity, these studies can contribute to the regional estimation of seismic hazard
Earthquake source parameters and scaling relationships in Hungary (central Pannonian basin)
Abstract Fifty earthquakes that occurred in Hungary (central
part of the Pannonian basin) with local magnitude ML
ranging from 0.8 to 4.5 have been analyzed. The digital
seismograms used in this study were recorded by six permanent
broad-band stations and twenty short-period ones at
hypocentral distances between 10 and 327 km. The displacement
spectra for P- and SH-waves were analyzed according
to Bruneâs source model. Observed spectra were corrected
for path-dependent attenuation effects using an independent
regional estimate of the quality factor QS. To correct spectra
for near-surface attenuation, the k parameterwas calculated,
obtaining it fromwaveforms recorded at short epicentral distances.
The values of the k parameter vary between 0.01 to
0.06 s with a mean of 0.03 s for P-waves and between 0.01
to 0.09 s with a mean of 0.04 s for SH-waves. After correction
for attenuation effects, spectral parameters (corner
frequency and low-frequency spectral level) were estimated
by a grid search algorithm. The obtained seismic moments
range from4.21Ă1011 to 3.41Ă1015 Nm (1.7â€Mw â€4.3).
The source radii are between 125 and 1343 m. Stress drop
values vary between 0.14 and 32.4 bars with a logarithmic
mean of 2.59 bars (1 bar = 105 Pa). From the results, a linear
relationship between local andmomentmagnitudes has been
established. The obtained scaling relations show slight evidence
of self-similarity violation. However, due to the high
scatter of our data, the existence of self-similarity cannot be
excluded
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