Oldřich Novotný

Northwestern Turkey Earthquakes and the Crustal Structure Inferred from Surface Waves Observed in Western Greece

Records of several earthquakes occurring in Turkey in 1999 obtained at broadband seismic stations in western Greece have been used to study the dispersion of surface waves, mainly Love waves. The observed group-velocity dispersion curves have been inverted into horizontally layered models of the Earths crust by a modified method of the single-parameter variation. As compared with a previous model for the territory of Greece, the dispersion data require significantly lower velocities in the uppermost crust and smaller crustal thickness. In particular, the resulting model displays S -wave velocities between 1.3 and 2.4 km/sec in the upper 2 km and a crustal thickness of about 33 km. Manuscript received 31 July 2000.

A preliminary seismic model for the region of the west-Bohemian earthquake swarms

SummaryA layered model of the crustal and upper mantle structure for the region of the West-Bohemian earthquake swarms is proposed. This model represents a compilation of the results of deep seismic soundings, surface-wave investigations, and some local seismic measurements in the western regions of the Bohemian Massif.

Partial derivatives of dispersion curves of love waves in a single-layered medium

ZusammenfassungEs werden die ersten und zweiten partiellen Ableitungen der Dispersionskurven von Love-Wellen im Einschichtenmilieu studiert. Die Berechnung der partiellen Ableitungen führt man nicht anhand numerischen Ableitens durch, sondern mit einer schnelleren und genaueren, auf dem Satz der impliziten Funktionen gegründeten Methode. Die sich aus dem Studium partieller Ableitungen für die Interpretation der beobachteten Dispersionskurven ergebenden Folgerungen werden diskutiert.

Dispersion of Rayleigh waves along the Prague-Warsaw profile

SummaryPhase velocities of Rayleigh waves propagating along the Prague-Warsaw profile have been determined. A layered model of the Earths crust and upper mantle, satisfying the observed dispersion of Rayleigh waves, has been derived. In constructing this model, the results of deep seismic soundings along international profile VII were also taken into account.

Verification of the Litho-spheric Structure along Profile Uppsala-Prague Using Surface Wave Dispersion

Experimental dispersion curves of Rayleigh and Love waves along the Uppsala-Prague profile have been determined using records of several Italian earthquakes. To interpret the dispersion data, results of previous geophysical investigations in this region were first analyzed. Seven blocks of the crust and upper mantle were distinguished along the profile on the basis of deep seismic sounding and other seismic data. Layered models were proposed for these blocks. Computation of Rayleigh and Love waves shows a large differentiation of theoretical dispersion curves for the northern (Precambrian) and southern (Palaeozoic) part of the profile. A laterally inhomogeneous model for theUppsala - Prague profile, composed of the seven blocks, satisfies the surface wave data for the profile. Moreover, a mean layered model for the whole profile has also been proposed.

Methods of computing the partial derivatives of dispersion curves

SummaryThree methods of computing the partial derivatives of dispersion curves are briefly described and compared: numerical differentiation, variational methods and an implicit function method.

Upper crustal structure of the western Corinth Gulf, greece, inferred from arrival times of the January 2010 earthquake sequence

The western part of the Corinth Gulf attracts attention due to its seismically active fault system and considerable seismic hazard. A moderate size earthquake occurred close to the town of Efpalio on January 18, 2010, followed by a sequence of smaller earthquakes. In the present paper we use this sequence to derive a local structural model for the region in the vicinity of Efpalio. The model is based on the minimization of traveltime residuals. In particular, we used arrival times from 51 selected events recorded on January 19 and 20 by at least 5 stations at epicentral distances less than about 25 km. A variant of the method of conjugate gradients has been used for this purpose. In comparison with several previous models, the new model is characterized by higher velocities to a depth of about 8 km. The velocity ratio in the model is vP / vS = 1.83. The hypocentres of the selected earthquakes lay at depths between about 5 and 9 km, but their distribution is rather irregular.

Low-frequency and high-frequency expressions for the reflection and transmission coefficients of seismic waves for transition layers

SummaryLow-frequency and high-frequency expressions are derived for the reflection and transmission coefficients of SH waves on transition layers, in which the modulus of torsion μ and density ϱ vary with depth only. Both the expressions are exact for any finite frequencies. However, the use of the former formulae is more convenient for low frequencies and, likewise, the latter formulae for high frequencies. Explicit expressions for several first terms of the expansions in terms of ω and 1/ω are given.

Earthquake location from P-arrival times only: problems and some solutions

Selected problems related to accurate hypocenter locations are discussed in the difficult case that only reliable P-wave readings are available. Near stations are usually only few, and often have a poor azimuthal coverage. As such, they are insufficient because the inversion is highly ill-posed, and the epicenter position strongly trades-off with depth. Thus more distant stations are also needed to obtain the correct epicenter. However, joint use of near and distant stations present another difficulty; it may yield a significantly incorrect depth estimate in case that the crustal model is not fully appropriate. In practice, the erroneous depth often remains unrecognized. An indication of the depth problem can be obtained by analyzing the travel-time residuals at individual stations. It is also useful to check fully independent depth estimates, for example those from the centroid-moment-tensor analysis. If the problematic crustal model is detected, and it is not easy to find a better one, the near- and distant station effects should be decoupled (a two-step location): the epicenter is calculated from all stations, kept fixed, and the source depth is grid-search beneath the epicenter by means of the near stations. The ideas are applied to the Mw 5.2 Efpalio (Western Greece) earthquake of January 18, 2010, and the following aftershock sequence.

Theoretical dispersion curves for the seismic profile Kašperské Hory (Czechoslovakia) — Ksiaz (Poland)

РезюмеРaссчumaны mеореmuческuе ¶rt;uсnерсuонные крuвые nоверхносmных сеŭсмuческuх волн ¶rt;ля nрофuляКНС-КSР. Рaссмamрuвaемaя мо¶rt;ель земноŭ коры основaнa нa резульmamaхглубuнного сеŭсмuческого зон¶rt;uровaнuя в¶rt;оль VII меж¶rt;унaро¶rt;ного nрофuля. Эma мо¶rt;ель можеm служumь нaчaльноŭ мо¶rt;елью в бу¶rt;ущuх эксnерuменmaльных uссле¶rt;овaнuях ¶rt;uсnерсuu в¶rt;оль nрофuляКНС-КSР.