Erhard Wielandt

Universität Stuttgart · Institute for Geophysics

We constructed a three-component combination seismometer and geodetic sensor suitable for borehole deployment. The instrument uses no electronics at depth in the borehole, rather it relies on optics. Two ∼40 cm pendulums suspended from two orthogonal axes with free periods slightly more than 1 s and a vertical mass-spring suspension with a free per...

We have measured the nonlinear distortion in six broadband seismometers on the vertical shake table at the Institute of Geophysics and Planetary Physics La Jolla: a vertical STS1, three STS2s, a CMG-3T, and a Trillium 240. In each case, low-frequency intermodulation of a two-tone signal was observed for six frequency pairs near 0.25, 0.5, 1, 2, 4,...

5.1 Overview There are two basic types of seismic sensors: inertial seismometers which measure ground motion relative to an inertial reference (a suspended mass), and strainmeters or extensometers which measure the motion of one point of the ground relative to another. Since the motion of the ground relative to an inertial reference is in most case...

Analysing magnetic field recordings from a quiet period in 2007 January we find that seismometers with a sensitivity to horizontal component of magnetic field larger than 0.2 ms-2T-1 would not be able to resolve the New Low Noise Model (NLNM) between 0.3 and 3 mHz (i.e. in the low-frequency normal-mode band). In a previous study the sensitivity to...

A bug in the code provided in the electronic supplement affects the computation of instrument noise by the Holcomb and Sleeman methods. The corrected code is supplied in the electronic supplement to this erratum.

We are developing a new vertical seismometer, motivated by a desire to have an instrument whose performance is similar to that of observatory sensors yet can operate within a borehole without electronics. This has led us to an all-optical seismometer consisting of a spring-suspended mass whose position is monitored interferometrically. We use a Mic...

The STS-1 VBB, widely viewed as the finest VBB sensor in the world, is currently the principal broad-band seismometer used by the Global Seismographic Network (GSN), GEOSCOPE, and several other global or regional seismic networks. Its continued operation is critical to future, fundamental research in a number of important disciplines within seismol...

In the 2-D acoustic case, the sound velocity of a heterogeneous medium can be determined from the amplitude and phase of almost any wavefield (but not from its phase alone) by inserting the wavefield into the Helmholtz equation and resolving for the wavenumber. Seismic surface waves in a laterally heterogeneous half-space do not obey the Helmholtz...

The STS-1 seismometer is currently the principal very broad-band (VBB) seismometer used in global or regional seismic networks operated by members of the Federation of Digital Broad-Band Seismograph Networks (FDSN). It is widely viewed as the finest VBB sensor in the world, Unfortunately, many of the STS-1's, which were manufactured and installed 1...

In the course of the upgrade of the Gräfenberg Array (GRF) from Streckeisen STS-1 seismometers with 20 sec free period to STS-2 seismometers with 120 sec free period the question of how best to install the sensors was reconsidered. It was understood early on that the Streckeisen STS-1 seismometers need elaborate shielding in order to reach their fu...

We present a 2-D reformulation of surface wave scattering theory in terms of potentials, which allows an extension of the Born single-scattering approach to include multiple forward scattering. No additional numerical effort compared to single scattering is required for a computation of the wavefield over the whole heterogeneous region. Born single...

As a model for the 2-D horizontal propagation of seismic surface waves, we study the propagation of non-plane acoustic waves in homogeneous and inhomogeneous media. We find that their phase velocity depends not only on the medium but also on the local geometry of the wavefield, especially on the distribution of amplitudes around the point of observ...

Seit 1994 betreibt das Monschauer St.-Michael-Gymnasium ein Schulseismometer, wissenschaftlich begleitet von Geophysikern der Universität Stuttgart. Seitdem werten Schüler Erdbeben rund um den Globus aus und werden Zeugen dramatischer Ereignisse. Mit der Konstruktion wurden drei Schüler 1996 Landessieger und Bundeszweite bei Jugend Forscht, in der...

Seismic Tomography Structure of the Crust in the Fennoscandian Shield T. Tiira, T. Hyvönen, K. Komminaho, A. Korja and P. Heikkinen Institute of Seismology, University of Helsinki, Helsinki, Finland A three-dimensional travel time tomography is applied to explosion data in order to derive a crustal velocity model beneath the central Fennoscandian S...

In 1992 M.W. Evans proposed a so-called O(3) symmetry of electromagnetic fields by adding a constant longitudinal "ghost field" to the well-known transversal plane em waves. He considered this symmetry as a new law of electromagnetics. Later on, since 2002, this O(3) symmetry became the center of his Generally Covariant Unified Field Theory which h...

Regional seismic tomography provides valuable information on the structure of shields, thereby gaining insight to the formation and stabilization of old continents. Fennoscandia (known as the Baltic Shield for its exposed part) is a composite shield for which the last recorded tectonic event is the intrusion of the Rapakivi granitoids around 1.6 Ga...

Few fundamental advances have been made in seismometers since the introduction of the broadband feedback systems nearly 1/4 century ago. In the intervening period, academic (and to a lesser extent industrial) research and developments on seismographic instrumentation has declined. Today, adequate sensors to meet the scientific requirements are in s...

A number of different geodynamic models have been proposed to explain the early tectonic evolution of the Baltic Shield. To provide additional geophysical constraints on these models, we performed a teleseismic tomography traveltime inversion for the central part of the Baltic Shield. The SVEKALAPKO project is focused on the investigation of the li...

The structure of the mantle transition zone between two seismic discontinuities at depths near 410 and 660 km is one of the most important issues to understand the Earth's dynamics. Most of what we know about this zone is based on seismic interpretation. Seismic waves observed in the distance range of about 15-28° turn in the transition zone and gi...

This chapter discusses the software for seismometer calibration and signal analysis. The chapter includes the various programs, which include: CALEX, DISPCAL, NOISECON, SINFIT, TILTCAL, and UNICROSP. CALEX determines parameters of the transfer function of a seismometer from the response to an arbitrary input signal (which must be recorded together...

Assessment of contributions from shallow lithosphere to teleseismic wave front distortion is a prerequisite for high-resolution regional teleseismic tomography. Several methods have been proposed in the past for the correction of these effects, e.g. application of station correction terms. We propose an approach that is independent of the subsequen...

This chapter focuses on the theory and usage of seismometers. It describes some general design principles along with precise methods for calibrating and testing. Seismometry refers to a technical discipline concerned with the detection and measurement of seismic ground motion. It comprises the design of seismographs, their calibration and installat...

Acceleration power spectral densities of vertical seismic noise at the best seismic stations show a minimum near 3 mHz. We suggest that this minimum is caused by a cancellation near this frequency of Newtonian attraction vs. free air and inertial effects exerted by atmospheric phenomena on the sensor mass. Simplistic models of atmospheric phenomena...

Broadband seismic recordings in the near-field of Strombolian explosions, at 500 m distance, show pronounced effects of tilt. The tilt signal is predominant in the horizontal components beyond about 50 s period while it is negligible in the vertical component. The waveform of the tilt signal at the seismometer output is a double time integral of th...

Im Heubachtal bei Schiltach im Schwarzwald, in einem alten Silberbergwerk 150 Meter unter Tage, stehen einige der empfindlichsten Seismographen Deutschlands. Wer allerdings meint, er könne dort feinmechanische Wunderwerke mit Dutzenden von Hebeln, Zahnrädern, Walzen und Federn besichtigen, wird enttäuscht. Erstens nämlich gibt es keine Besichtigung...

Teleseismic surface waves in general strongly deviate from plane waves as is evident from the analysis of surface-wave data recorded with dense networks. This causes conventional, ray-based tomographic techniques to break down if applied to network surface-wave data. We present a new inversion method based on the acoustic-wave equation and applicab...

Seismic surface waves exhibit much more complicated wavefields than is commonly assumed. We are led to this conclusion after analysing 90 teleseismic events recorded at on average eight broad-band stations in Southern Germany. Large amplitude and phase fluctuations across the network are observed which, as we show, are definitely not due to instrum...

The phase velocity dispersion of Rayleigh waves for the Moxa-Vienna (MOX-VIE) and Moxa-Kapersk Hory (MOX-KHC) profiles, and of both Rayleigh and Love waves for the Kapersk Hory-Ksi (KHC-KSP) profile have been measured and inverted into models of shearwave velocity vs. depth. The three paths cross, respectively, the central part of the Bohemian Mass...

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This chapter deals with the influence of diffracted waves on tomographic observations. Probably most workers in tomography are aware of the existence of such waves and of their potential to interfere with the direct wave on which the tomographic interpretation is based. Strong diffraction effects are expected when the scale of heterogeneity is in t...

A digital seismograph is presented which uses only one sensor and one signal data stream for each component of ground motion to record nearly the entire teleseismic spectrum. This system is called very-broad-band or VBB. As sensors the STS-1 (leaf-spring) seismometers (Wielandt and Streckeisen, 1982) are used. Their feedback circuit has been modifi...

The phase dispersion of fundamental-mode Rayleigh waves from the second Gazli earthquake has been measured at periods between 40 and 400 s between Los Angeles and the South Pole. Over most of its length, the path between the two stations is parallel and close to the East Pacific Rise. The phase velocities we have observed are significantly lower th...

The precision of measurement of surface-wave phase velocities at very long periods has reached a point where the exact, rather than asymptotic, form of the spherical harmonics must be considered in order to compute theoretical phase velocities or phase delays. The zeroth-order (i.e. constant) polar phase shift afterBrune et al. (1961) applies only...

Some technical problems commonly encountered in marine heat-flow measurements have been overcome with a digitally recording seabottom probe containing in its pressure case no moving parts except a stepper relay. The probe stores digitally at regular time intervals the resistances of 11 thermistors in a 240-word CMOS memory. After return to the surf...

A long-period seismograph has been developed where the galvanometer photographic recording has been replaced by an electronic amplifier-filter circuit and ink recording, at comparable cost. The system has been tested carefully and found to be superior to conventional systems in some respects, especially in the stability of the transfer function and...

Thesis (doctoral)--Universität Karlsruhe, 1972.