Lunar subsurface investigated from correlation of seismic noise

Classical and Quantum Gravity, 2002

Ocean waves interacting in shallow water at the shore generate land waves propagating inland. To study these waves vertical, horizontal and tilt seismic noise were measured simultaneously at one location. Vibration isolators designed for gravitational wave research were used for detection. Cross-correlation was calculated between the above components. We found correlations between all of them. But, only the correlation between horizontal and vertical motion could possibly be addressed to land waves..

Journal of Geophysical Research: Solid Earth, 2009

Seismic noise cross correlations have become a novel way of probing the elastic structure of the Earth without relying on an often highly nonuniform and sporadic distribution of earthquakes. By circumventing this restriction, one can determine the elastic Green's function between any two points where instruments exist. For tomography, this will allow for a larger distribution of crossing paths and therefore better resolution in the inversions. One can also monitor the same station pair Green's functions for changes in the state of the Earth, an application that has been employed in volcanic monitoring. One limitation of this cross‐correlation technique is that the input time series are frequently very long to recover high‐fidelity signals. We present two time‐frequency stacking algorithms to denoise the correlated signals and to alleviate this problem; increasing signal‐to‐noise ratios allows for high‐fidelity Green's functions to be constructed from shorter time series....

Science, 2005

Journal of Physics: Conference Series, 2008

The correlation of ambient vibrations of the Earth yields the impulse response between two passive sensors as if one was a source. This provides the opportunity to image the Earth beneath regional seismic arrays. In this paper, we present imaging of the lithosphere in Europe based on surface Rayleigh waves extracted from continuous record of the seismic noise. We also recall a brief history of passive imaging in seismology. The link between correlations and the green function is investigated from a mathematical point of view, and through laboratory experiments.

We present here a global analysis showing that wave paths probing the deepest part of the Earth can be obtained from ambient noise records. Correlations of seismic noise recorded at sensors located various distances apart provide new virtual seismograms for paths that are not present in earthquake data. The main arrivals already known for earthquake data are also present in teleseismic correlations sections, including waves that have propagated through the Earth's core. We present examples of applications of such teleseismic correlations to lithospheric imaging, study of the core mantle boundary or of the anisotropy of the inner core.

Chinese Science Bulletin, 2008

We attempted to determine the first three-dimensional P and S wave velocity and Poisson's ratio structures of the lunar crust and mantle down to 1000 km depth under the near-side of the Moon by applying seismic tomography to the moonquake arrival-time data recorded by the Apollo seismic network operated during 1969 to 1977. Our results show that significant lateral heterogeneities may exist in the lunar interior. Because there is no plate tectonics in the Moon, the lateral heterogeneities may be produced at the early stage of the Moon formation and evolution, and they have been preserved till today. There seems to be a correlation between the distribution of deep moonquakes and lateral velocity variations in the lunar lower mantle, suggesting that the occurrence of deep moonquakes may be affected by the lunar structural heterogeneity in addition to the tidal stresses. Although this is an experimental work and the result is still preliminary, it indicates that tomographic imaging of the lunar interior is feasible.

Journal of Geophysical Research, 2008

1] By applying the noise cross-correlation technique to Apollo 17 Lunar Seismic Profiling Experiment (LSPE) data, we discovered temporal changes in Rayleigh-wave group velocity within a diurnal cycle (29.53 d). Assuming that this phenomenon is caused by density and seismic parameter changes due to temperature, we formulated an inverse problem. Thermal diffusivity serves as the key parameter for this problem because it controls the depth penetration of temperature change. The results of inversion indicate that a typical number for the thermal diffusivity of terrestrial rocks (k % 10 À6 m 2 /s) is too large to fit the data. Our preferred value is about k % 10 À7 (m 2 /s), although the inversion alone cannot discriminate among the values below this number. Differences between this estimate and a lower estimate (k % 10 À8 m 2 /s) by Langseth et al. may indicate the significance of radiation for thermal transfer in the upper-most lunar crust. We also find a direct correlation between the Rayleigh-wave amplitudes and the statistics of thermal moonquakes, both of which change with the diurnal periodicity and peak at sunset. This implies that thermal moonquakes are the source of valuable seismic noise, lending strong support to an idea proposed by Larose et al. This is in contrast to the terrestrial situation where the ocean-generated noise plays a critical role in the cross-correlation approach. The noise correlation approach is potentially useful for many planets which undergo wide swings in surface temperature and thus potentially have thermal quakes.

Geochemistry, Geophysics, Geosystems, 2013

Ambient-noise seismology is of great relevance to high-resolution crustal imaging, thanks to the unprecedented dense data coverage it affords in regions of little seismicity. Under the assumption of uniformly distributed noise sources, it has been used to extract the Greens function between two receivers. We determine the imprint of this assumption by means of wave propagation and adjoint methods in realistic 3D Earth models. In this context, we quantify the sensitivity of ambient-noise cross correlations fromc e n t r a l Europe with respect to noise-source locations and shear wavespeed structure.

Earthquake Science, 2011

Geochemistry, Geophysics, Geosystems, 2008

1] We perform ambient noise tomography of China using data from the China National Seismic Network and surrounding global and regional stations. For most of the station pairs, we retrieve good Rayleigh waveforms from ambient noise correlations using 18 months of continuous data at all distance ranges across the entire region (over 5000 km) and for periods from 70 s down to about 8 s. We obtain Rayleigh wave group velocity dispersion measurements using a frequency-time analysis method and invert for Rayleigh wave group velocity maps for periods from 8 s to 60 s. The tomographic maps display significant features that correlate with surface geology. Major basins, including Tarim, Junggar, Qadaim, Sichuan, Bohai-Wan, and Songliao, are all well delineated by slow group velocities at shorter periods (10 to 20 s). The overall trend of crustal thickening from east to west is well represented by group velocity decreases from east to west at periods around 30 s.