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Crustal Attenuation Characteristics in Northwestern Turkey in the Range from 1 to 10 Hz

¹ Istituto Nazionale di Geofisica e Vulcanologia
via Bassini 15
20133 Milano, Italy
 (D.B.)

² GeoForschungsZentrum Potsdam
Telegrafenberg
14473 Potsdam, Germany
 (S.P., H.G., C.M.)

³ Ministry of Public Works and Settlement
General Directorate of Disaster Affairs
Earthquake Research Department
P.O. Box 763
Ankara, Turkey
 (S.K.)

View larger version (26K): [in this window] [in a new window]   Figure 1. Top: Earlier attenuation studies performed in Turkey. (1) Akinci and Eyidogan (1996); (2) Grosser et al. (1998); (3) Akinci and Eyidogan (2000); (4) Akyol et al. (2002); (5) Kaslilar-Özcan et al. (2002); (6) Gündüz et al. (1998); (7) Akinci et al. (2004); (8) this study. Bottom: the region investigated in the present work and the main alluvial basins (gray regions).

View larger version (26K): [in this window] [in a new window]   Figure 2. Ray-path coverage relevant to the utilized data set. Triangles and circles represent stations and events, respectively.

View larger version (31K): [in this window] [in a new window]   Figure 3. Resolution matrix.

View larger version (17K): [in this window] [in a new window]   Figure 4. Unit covariance matrix. Examples of the diagonal elements are shown in the inset in the top frame. In the bottom frame, a portion of the matrix is enlarged (row and column values are reported on the axes).

View larger version (25K): [in this window] [in a new window]   Figure 5. Spectral attenuation-distance curves, logA(f, r), for P and S waves against hypocentral distance for frequencies ranging from 1 to 10 Hz (solid line for P wave and dotted line for S wave).

View larger version (49K): [in this window] [in a new window]   Figure 6. Spectral amplitudes of records for the events with 2.5 ML 3 (gray circle) versus hypocentral distance, at the frequencies 2, 5, and 10 Hz. The left frames are for P waves, the right ones for S waves. The solid curves are logA(f, r) obtained from inversion performed at the corresponding frequency. An arbitrary offset has been added to the spectral-amplitude data to make the comparison easier.

View larger version (47K): [in this window] [in a new window]   Figure 7. Quality factor Qp (dotted lines and gray bars), Qs (thin lines and black bars), and geometrical spreading n versus frequency for distance from 10 to 38 km (left frames) and from 60 to 80 km (right frames). The mean ±2 are shown. For P waves, the results for frequencies smaller than 2 Hz (gray shaded area) are not reliable due to the low signal-to-noise ratio. In the left panel, results of fit (thick lines for QS and gray lines for QP) are shown.

View larger version (31K): [in this window] [in a new window]   Figure 8. QS/QP ratio versus frequency for different selected distances. The thick lines indicate the ratio obtained when considering the average quality factor for each distance range, as shown in Figure 7. The horizontal dotted lines indicate the reference values (see text).

View larger version (44K): [in this window] [in a new window]   Figure 9. Average (thin lines) ±1 standard deviation (gray area) integrated energy versus distances, at frequencies 1.6, 3.2, and 8 Hz; E1, E2, and E3 are the integrated energy for three different lapse times. The energy is corrected for the geometrical spreading (4r2) and normalized to coda (Aki, 1980). The thick lines represent the best- fit solution obtained using the Monte Carlo method (Hoshiba, 1991), corresponding to the B0, pair indicated inside each panel. For frequency 1.6 Hz (top-left panel) the dotted line corresponds to the best-fit solution obtained by applying the Hoshiba (1997) method to the model described in Table 2. In the bottom-right panel, (dotted line), (dashed line), and (continuous line) versus frequency are compared to QS(f) obtained via the spectral inversion for distance in the range 10–38 km (vertical bars) and 60–80 km (gray vertical bars).

View larger version (48K): [in this window] [in a new window]   Figure 10. Residuals normalized to their minimum, computed at 1.6 Hz (left) and 8 Hz (right) for several B0 pairs. In the bottom panels, the pairs that give residuals within 10% of the minimum are shown. In the top panels, the white crosses indicate the minimum residual.

View larger version (32K): [in this window] [in a new window]   Figure 11. Normalized synthetic SH seismograms obtained by applying the method described by Wang (1999) for the model given in Table 2. The source is at 10 km depth. In each panel, the epicentral distance and the absolute value of the maximum amplitude, expressed in m/sec, before normalization are shown.