seismic inteffer。metry and ambient n。ise t。m。graphy in East ASia

Earth History of Asia- II October 31 - November 3, Niigata, Japan
Seismic interferometry and ambient noise tomography in East Asia
KANG, Tae-Seob 1'
Department of Earth and Environmental Sciences, Pukyong National University, Busan 608-737,
[email protected]
Seismic imaging methods based on recordings of earthquakes suffer from various
limitations. Above all, their resolution tends to degrade in areas of low seismicity, far
斤om plate boundaries or other tectonically active areas. Waveforms from remote
earthquakes are poor at high frequencies, due to the attenuation and scattering of
waves along paths between sources and stations. This results in a low-resolution
tomography with traditional surface waves.
Nowadays most of the seismological networks produce continuous records of
ground movement. Huge amounts of data are accumulated and most of them are full of
so-called seismic background noise that corresponds to the seismic waves produced by
natural processes or human activity. The passive imaging is based on the possibility of
extracting consistent information on the seismic wave field between two sensors from
the recordings of ambient noise.
The existence of correlation between seemingly random signals recorded at
distant stations was first shown with the multiply diffracted wave coda (Campillo and
Paul, 2003). The correlation is considered to be the Green s function that is the
response of the Earth between two points, from which we can measure the travel time.
Shapiro and Campillo (2004) has successfully applied the same approach to recordings
of ambient noise and has opened the way for many applications (e.g., Kang and Shin,
2006; Choi et al., 2009).
In many recent studies where the noise was used to obtain the seismic response
between two points, coherent waves were extracted from the noise even though at first
glance, these coherent signals are hidden deep in an incoherent noise. One of concerns
among those applications is the imaging of structures at different scales. Here the noise
reduces the gap between spatial resolution methods based on earthquakes and active
sources. Firstly, correlation methods used in seismology allow waves between stations
near higher frequency than what is possible with remote earthquakes. The crust and
upper mantle are now commonly imaged, mainly with surface waves, at scales ranging
from thousands of kilometers to tens of meters. In addition to prospecting, correlations
Earth History of Asia- II October 31 - November 3, Nngata, Japan
can extend the analysis to lower frequencies compared to conventional active methods.
In this presentation, some studies on seismic tomography using ambient noise
cross-correlation in East Asia are introduced in various scales.
Campillo, M. and Paul, A., 2003, Long-range correlations in the diffuse seismic coda.
Science, 299, 547-549.
Choi, J., Kang, T.-S. and Baag, C.-E., 2009, Three-dimensional surface wave
tomography for the upper crustal velocity structure of southern Korea using seismic
noise correlations. Geosciences Journal, 13, 423-432.
Kang, T.-S. and Shin, J. S., 2006, Surface-wave tomography from ambient seismic
noise of accelerograph networks in southern Korea. Geophysical Research Letters,
33, L17303, doi:10.1029/2006GLO27044.
Shapiro, N. M. and Campillo, M., 2004, Emergence ofbroadband Rayleigh waves from
correlations of the ambient seismic noise. Geophysical Research Letters, 31,
L07614, doi:10.1029/2004GL019491.