%0 Conference Paper %1 wegler_etal:1999a %A Wegler, U. %A Riedel, C. %A Maercklin, N. %A Lühr, B. G. %A Rabbel, W. %A Zschau, J. %B Journal of Conference Abstracts %D 1999 %K geophysics myown seismics %T Scattering and absorption of seismic waves at Merapi volcano %V 4 %X Within the Indonesian German MERAPI project the seismic structure of the Merapi Volcano is investigated with an active seismic experiment. First seismic profiling was performed along 4 profiles arranged radially with respect to the summit. Each profile consists of 30 3-component seismometers with a station spacing of 100 m. As a seismic source, a 2.5 l mudgun was placed in three different water basins at a distance of 5 km from the summit. This special seismic source has a well defined spectral characteristic and high repetition accuracy. Along the 3 km long near-source profiles we observed refracted waves. The corresponding 1D depth profiles show low-velocity surface layers of some hundred m/s P-wave velocity. A greater depth the P-wave velocity increases to approximately 3000 m/s. The volcanic strata leads to strong scattering and absorption effects. A significant decrease of the main signal frequency from approximately 10 Hz to 5 Hz between 0 km and 3 km offset can be observed. This frequency shift coincides with the formation of a long coda with maximum amplitudes several seconds after the first break. The coda wavefield is mainly incoherent, which suggests some sort of random character of signal formation. We use randomly distributed scatterers to model the seismogram envelopes and to determine scattering parameters as well as Coda-Q-values. An analysis in the frequency-wavenumber domain shows, however, that besides the incoherent energy, the interference of coherent waves travelling back and forth along the profile also contibutes to the coda. We conclude that to understand the mechanisms of the natural volcanic seismic sources of Merapi, scattering and absorption effects along the propagation path must be considered.

@inproceedings{wegler_etal:1999a, abstract = {Within the Indonesian German MERAPI project the seismic structure of the Merapi Volcano is investigated with an active seismic experiment. First seismic profiling was performed along 4 profiles arranged radially with respect to the summit. Each profile consists of 30 3-component seismometers with a station spacing of 100 m. As a seismic source, a 2.5 l mudgun was placed in three different water basins at a distance of 5 km from the summit. This special seismic source has a well defined spectral characteristic and high repetition accuracy. Along the 3 km long near-source profiles we observed refracted waves. The corresponding 1D depth profiles show low-velocity surface layers of some hundred m/s P-wave velocity. A greater depth the P-wave velocity increases to approximately 3000 m/s. The volcanic strata leads to strong scattering and absorption effects. A significant decrease of the main signal frequency from approximately 10 Hz to 5 Hz between 0 km and 3 km offset can be observed. This frequency shift coincides with the formation of a long coda with maximum amplitudes several seconds after the first break. The coda wavefield is mainly incoherent, which suggests some sort of random character of signal formation. We use randomly distributed scatterers to model the seismogram envelopes and to determine scattering parameters as well as Coda-Q-values. An analysis in the frequency-wavenumber domain shows, however, that besides the incoherent energy, the interference of coherent waves travelling back and forth along the profile also contibutes to the coda. We conclude that to understand the mechanisms of the natural volcanic seismic sources of Merapi, scattering and absorption effects along the propagation path must be considered.}, added-at = {2012-09-01T13:08:21.000+0200}, author = {Wegler, U. and Riedel, C. and Maercklin, N. and L\"{u}hr, B. G. and Rabbel, W. and Zschau, J.}, biburl = {https://www.bibsonomy.org/bibtex/2fb688d7f9d2640bb67387f888c5964c8/nilsma}, booktitle = {Journal of Conference Abstracts}, interhash = {53a005063746dbe2a0522ccc268139a8}, intrahash = {fb688d7f9d2640bb67387f888c5964c8}, keywords = {geophysics myown seismics}, organization = {European Union of Geosciences}, timestamp = {2021-02-09T13:56:15.000+0100}, title = {Scattering and absorption of seismic waves at Merapi volcano}, volume = 4, year = 1999 }