ALBERT

Description: Ambient noise tomography is used to retrieve Rayleigh wave group and phase velocity variations in the period range of 8–40 s based on the vertical component of cross-correlation functions from permanent broad-band and mid-band seismometers across the Iranian Plateau. The iterative, non-linear inversion method of fast marching surface tomography (FMST) is employed to produce 2-D group and phase velocity maps. Shear wave velocities are also estimated using a linear least-square method. Unlike most previous largescale tomographic results, our group, phase and shear wave velocity estimations, emphasize low velocity crustal structure (up to 50 km depth) beneath Zagros Fold and Thrust Belt (ZFTB) and Sanandaj-Sirjan metaphormic Zone (SSZ). The suture zone resulting from the subduction of the Arabian plate under the Central Iran is inferred along the boundary of SSZ and Urmieh-Dokhtar Magmatic Arc (UDMA). The velocity patterns show the main sedimentary basins, and reveal lateral velocity changes indicating the crustal thickening beneath ZFTB, SSZ and Lut Desert (LD), and the crustal thinning beneath Kavir Desert (KD) and UDMA are well inferred. A prominent low velocity is persistent in the whole crust beneath the central part of Alborz mountain range with high topography, and we suggest that it is likely due to elevated crustal temperatures within thin lithosphere.

Description: De novo mutations of the voltage-gated sodium channel gene SCN8A have recently been recognized as a cause of epileptic encephalopathy, which is characterized by refractory seizures with developmental delay and cognitive disability. We previously described the heterozygous SCN8A missense mutation p.Asn1768Asp in a child with epileptic encephalopathy that included seizures, ataxia, and sudden unexpected death in epilepsy (SUDEP). The mutation results in increased persistent sodium current and hyperactivity of transfected neurons. We have characterized a knock-in mouse model expressing this dominant gain-of-function mutation to investigate the pathology of the altered channel in vivo . The mutant channel protein is stable in vivo . Heterozygous Scn8a N1768D/+ mice exhibit seizures and SUDEP, confirming the causality of the de novo mutation in the proband. Using video/EEG analysis, we detect ictal discharges that coincide with convulsive seizures and myoclonic jerks. Prior to seizure onset, heterozygous mutants are not defective in motor learning or fear conditioning, but do exhibit mild impairment of motor coordination and social discrimination. Homozygous mutant mice exhibit earlier seizure onset than heterozygotes and more rapid progression to death. Analysis of the intermediate phenotype of functionally hemizygous Scn8a N1768D/– mice indicates that severity is increased by a double dose of mutant protein and reduced by the presence of wild-type protein. Scn8a N1768D mutant mice provide a model of epileptic encephalopathy that will be valuable for studying the in vivo effects of hyperactive Na v 1.6 and the response to therapeutic interventions.

Description: The capability of seismic interferometry to create virtual sources atreceiver sites from records of ambient seismic noise is used for seismic monitoringand tomography of different targets.We present hardware developed specificallyfor the needs of seismic data acquisition in the context of monitoring and ambientnoise tomography. Digitizers are capable of continuous recording and real timewireless data transmission in self organizing meshes to allow for robust telemetry indifficult circumstances such as cities or landslides that may cause the loss of stations.A software tool is described that implements required processing and analysis proceduresfor the interferometric processing.We have applied the novel 3Dambient noisesurface wave tomography approach to the Issyk-Ata fault in Kyrgyzstan. It showsthat seismic interferometry can successfully be used for structural investigations onlength scales of only 100 m. The method uses 3D sensitivity kernels for a singlestepinversion of phase velocity dispersion curves for subsurface S-wave velocitystructure and incorporates topography. We recover lateral differences in sedimentvelocities and an offset of the bedrock depth across the fault. Applications of interferometricmonitoring to the geological CO2 storage test site in Ketzin (Germany)and to the Piton de la Fournaise volcano (La Reunion island) emphasize the valueof this approach. At Ketzin site we identify variations of the subsurface velocitiesthat are correlated with changes in the ground water level and mask potential signalsfrom the reservoir depth. At Piton de la Fournaise volcano, seismic velocity changesare linked to volcanic processes as shown by comparison with surface displacementand seismicity that are typically used to characterize volcanic activity.We observe aclear distinction between phases of inflation prior to eruptions and deflation duringperiods of quiescence.

Description: Measurements of rotational motions of the seismic wave-field have recently shown a high amount of rotational energy also in the coda of seismic events. Especially the rotational motion in the P-wave coda bears interesting information as it can only be excited by scattering of the wave-field at 3D heterogeneities. It indicates the conversion from P to S energy in the Earth's subsurface and consequently the scattering of high-frequency seismic waves. A suitable method to describe the propagation and scattering of high-frequency waves is the radiative transfer theory (RTT). RTT describes the spatial and temporal distribution of seismic energy emitted from a seismic source. It considers scattering and mode conversions between P, SV and SH polarizations. It also includes the angular dependent scattering pattern derived from the Born approximation. The RTT does not contain any phase information of the seismic waves. Therefore the energy of superimposing waves is considered additive and no interferences between the seismic signals are treated. This makes the RTT a very useful tool for the description of scattered waves. It has recently been shown that the RTT is a powerful method to compute seismogram envelopes for the three translational components of the seismic wave-field. In this study we extend the capabilities of the method to model six-component seismogram envelopes in an elastic medium with randomly distributed velocity and density perturbations. The approach implements Monte Carlo (MC) solutions to the radiative transfer equation. The three additional rotational components can provide independent information about the Earth's structure and the seismic source. They can for example be used to further constrain scattering properties and thus help to discriminate between intrinsic and scattering attenuation. The results of the MC simulations are verified by comparison with 3D full wave-field finite difference simulations. Six-component seismogram envelopes from the two different approaches are compared. We obtain reasonable agreement not only for the translational components but also for the rotational energy. In conclusion, the RTT is a useful approach to model the six-component seismogram envelopes of Seismologie - Poster – 301 high-frequency wave-fields from the initial onset of the direct P-wave to the later part of the S-wave coda in random elastic media.

Description: The 3D structure of the upper crust beneath west Bohemia/Vogtland region, analyzed with travel time tomography and ambient noise surface wave tomography using existing data. This region is characterized by a series of phenomena like occurrence of repeated earthquake swarms, surface exhalation, CO2 enriched fluids, mofettes, mineral springs and enhanced heat flow, and has been proposed as an excellent location for an ICDP drilling project targeted to a better understanding of the crust in an active magmatic environment. We performed a 3D tomography using P-and S-wave travel times of local earthquakes and explosions. The data set were taken from permanent and temporary seismic networks in Germany and Czech Republic from 2000 to 2010, as well as active seismic experiments like Celebration 2000 and quarry blasts. After picking P and S wave arrival times, 399 events which were recorded by 9 or more stations and azimuthal gap〈160[U+25E6] were selected for inversion. A simultaneous inversion of P and S wave 1D velocity models together with relocations of hypocenters and station corrections was performed. The obtained minimum 1D velocity model was used as starting model for the 3D Vp and Vp/Vs velocity models. P and S wave travel time tomography employs damped least-square method and ray tracing by pseudo-bending algorithm. For model parametrization different cell node spacings have been tested to evaluate the resolution in each node. Synthetic checkerboard tests have been done to check the structural resolution. Then Vp and Vp/Vs in the preferred 3D grid model have been determined. Earthquakes locations in iteration process change till the hypocenter adjustments and travel time residuals become smaller than the defined threshold criteria. Finally the analysis of the resolution depicts the well resolved features for interpretation. We observed lower Vp/Vs ratio in depth of 5-10 km close to the foci of earthquake swarms and higher Vp/Vs ratio is observed in Saxoturingian zone and surrounding area. Surface wave tomography using ambient noise provides additional constraints on shear velocities. The detailed knowledge of the 3D structure is essential to select the optimal future borehole locations. we use the vertical and transverse component ambient noise data to estimate both Rayleigh and Love waves from ambient noise cross-correlation waveforms to investigate the crustal seismic structure of W-Bohemia/Vogtland. More than 2000 Rayleigh and Love group-velocity dispersion curves are obtained by time-frequency analysis of stacked ambient noise cross-correlation functions between station pairs. We used the data between 2002 and 2004 recorded at 43 seismic stations from BOHEMA experiment and between 2006 and 2008 recorded at 79 seismic stations from permanent station networks of Germany, Czech Academy of Sciences (WEBNET) and PASSEQ experiments. At each period between 1 and 10 s, group velocity maps are constructed, all corresponding to different sampling depths, and thus together giving an indication of the 3D shear wave velocity structure extending to a depth of about 15 km.

Description: The information contained in the high frequency seismic wave field extends beyond travel times. Omnipresent coda waves reflect the structural heterogeneity of the medium that leads to complex propagation paths of scattered waves. Analysis of these coda waves can therefore help to characterize the structure of the medium on length scales that is not accessible by traditional tomographic techniques. Wave propagation at regional distances has been used successfully in this context. Seismologie - Naturgefahren und Geophysik – 281 Here we focus on global distances. We present an algorithm to model the high frequency seismic energy propagation in a spherically symmetric Earth model such as ak135 with additional small scale heterogeneity. The algorithm solves the radiative transfer equation by means of a Monte-Carlo simulation of individual energy particles. The simulation results are contrasted with envelope stacks of global teleseismic records.

Description: Recent measurements of rotational motions of the seismic wave field have shown a significant amount of rotational energy also in the coda of seismic events. In particular the rotational motion in the P-wave coda bears interesting information as it can only be excited by scattering of the wave-field at 3D heterogeneities. This rotational motion clearly indicates the conversion from P to S energy in the Earth’s subsurface and subsequently the scattering of high-frequency seismic waves. A suitable method to describe this phenomena is the Radiative Transfer Theory (RTT). RTT describes the spatial and temporal distribution of seismic energy emitted from a seismic source. It considers scattering and mode conversions between P, SV and SH polarizations. It also includes the angular dependent scattering pattern derived from the Born approximation. The RTT approach implements Monte Carlo (MC) solutions to the radiative transfer equation. Since the RTT does not contain any phase information of the seismic waves, the energy of superimposing waves can be considered additive and no interferences between the seismic signals are treated. This makes the RTT a very useful tool for the description of scattered waves. It has recently been shown that the RTT is a powerful method to compute seismogram envelopes for the three translational components of the seismic wave-field. In this study we additionally compute the three rotational components and therefore extend the capabilities of the method to model six-component seismogram envelopes in an elastic medium with randomly distributed velocity and density perturbations. The three additional rotational components can provide independent information about the Earth’s structure and the seismic source. For instance they can be used to further constrain scattering properties and thus help to discriminate between intrinsic and scattering attenuation. The results of the MC simulations are verified by comparison with 3D full wave-field finite difference simulations. Six-component seismogram envelopes from the two different approaches are compared. A reasonable agreement for the translational components as well as for the rotational energy is obtained. In conclusion, the RTT is a useful approach to model the six-component seismogram envelopes of high-frequency wave-fields from the initial onset of the direct P-wave to the later part of the S-wave coda in random elastic media.