Publication Date:
2017-04-04
Description:
By using small-to-moderate-sized earthquakes located within ~200 km of San
Francisco, we characterize the scaling of the ground motions for frequencies ranging
between 0.25 and 20 Hz, obtaining results for geometric spreading, Q(f), and site
parameters using the methods of Mayeda et al. (2005) and Malagnini et al. (2004). The
results of the analysis show that, throughout the Bay Area, the average regional
attenuation of the ground motion can be modeled with a bilinear geometric spreading
function with a 30 km crossover distance, coupled to an anelastic function
!
exp "
#fr
$Q( f )
%
&
'
(
)
* ,
where: Q(f)=180 f 0.42. A body-wave geometric spreading, g(r)= r -1.0, is used at short
hypocentral distances (r 〈 30 km), whereas g(r)= r -0.6 fits the attenuation of the spectral
amplitudes at hypocentral distances beyond the crossover.
The frequency-dependent site effects at 12 of the Berkeley Digital Seismic
Network (BDSN) stations were evaluated in an absolute sense using coda-derived source
spectra.
Our results show: i) the absolute site response for frequencies ranging between 0.3 Hz
and 2.0 Hz correlate with independent estimates of the local magnitude residuals (dML)
for each of the stations; ii) moment-magnitudes (MW) derived from our path and sitecorrected
spectra are in excellent agreement with those independently derived using fullwaveform
modeling as well as coda-derived source spectra; iii) we use our weak-motionbased
relationships to predict motions region wide for the Loma Prieta earthquake, well
above the maximum magnitude spanned by our data set, on a completely different set of
stations. Results compare well with measurements taken at specific NEHRP site classes;
iv) an empirical, magnitude-dependent scaling was necessary for the Brune stress
parameter in order to match the large magnitude spectral accelerations and peak ground
velocities with our weak-motion-based model.
Description:
Submitted
Description:
open
Keywords:
Ground motion
;
04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
manuscript
Format:
6679919 bytes
Format:
application/pdf
Permalink
