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Catherine L. Johnson - One of the best experts on this subject based on the ideXlab platform.

  • Shallow seismic activity and young thrust faults on the Moon
    Nature Geoscience, 2019
    Co-Authors: Thomas R. Watters, Renee C. Weber, Geoffrey C. Collins, Ian J. Howley, Nicholas C. Schmerr, Catherine L. Johnson
    Abstract:

    Shallow Moonquakes detected at four Apollo landing sites between 1969 and 1977 occurred during maximum stress and in close proximity to young faults, suggesting that the Moon is tectonically active, according to reanalyses of the seismic data and tidal force modelling. The discovery of young thrust faults on the Moon is evidence of recent tectonic activity, but how recent is unknown. Seismometers at four Apollo landing sites recorded 28 shallow Moonquakes between 1969 and 1977. Some of these shallow quakes could be associated with activity on the young faults. However, the epicentre locations of these quakes are poorly constrained. Here we present more-accurate estimates of the epicentre locations, based on an algorithm for sparse seismic networks. We found that the epicentres of eight near-surface quakes fall within 30 km of a fault scarp, the distance of the expected strong ground shaking. From an analysis of the timing of these eight events, we found that six occurred when the Moon was less than 15,000 km from the apogee distance. Analytical modelling of tidal forces that contribute to the current lunar stress state indicates that seven near-apogee events within 60 km of a fault scarp occur at or near the time of peak compressional stresses, when fault slip events are most likely. We conclude that the proximity of Moonquakes to the young thrust faults together with evidence of regolith disturbance and boulder movements on and near the fault scarps strongly suggest the Moon is tectonically active.

  • A simple physical model for deep moonquake occurrence times
    Physics of the Earth and Planetary Interiors, 2010
    Co-Authors: Renee C. Weber, B. G. Bills, Catherine L. Johnson
    Abstract:

    Abstract The physical process that results in Moonquakes is not yet fully understood. The periodic occurrence times of events from individual clusters are clearly related to tidal stress, but also exhibit departures from the temporal regularity this relationship would seem to imply. Even simplified models that capture some of the relevant physics require a large number of variables. However, a single, easily accessible variable – the time interval I(n) between events – can be used to reveal behavior not readily observed using typical periodicity analyses (e.g., Fourier analyses). The delay-coordinate (DC) map, a particularly revealing way to display data from a time series, is a map of successive intervals: I(n + 1) plotted vs. I(n). We use a DC approach to characterize the dynamics of moonquake occurrence. Moonquake-like DC maps can be reproduced by combining sequences of synthetic events that occur with variable probability at tidal periods. Though this model gives a good description of what happens, it has little physical content, thus providing only little insight into why Moonquakes occur. We investigate a more mechanistic model. In this study, we present a series of simple models of deep moonquake occurrence, with consideration of both tidal stress and stress drop during events. We first examine the behavior of inter-event times in a delay-coordinate context, and then examine the output, in that context, of a sequence of simple models of tidal forcing and stress relief. We find, as might be expected, that the stress relieved by Moonquakes influences their occurrence times. Our models may also provide an explanation for the opposite-polarity events observed at some clusters.

  • Constraints on deep moonquake focal mechanisms through analyses of tidal stress
    Journal of Geophysical Research, 2009
    Co-Authors: Renee C. Weber, B. G. Bills, Catherine L. Johnson
    Abstract:

    [1] A relationship between deep moonquake occurrence and tidal forcing is suggested by the monthly periodicities observed in the occurrence times of events recorded by the Apollo Passive Seismic Experiment. In addition, the typically large S wave to P wave arrival amplitude ratios observed on deep moonquake seismograms are indicative of shear failure. Tidal stress, induced in the lunar interior by the gravitational influence of the Earth, may influence moonquake activity. We investigate the relationship between tidal stress and deep moonquake occurrence by searching for a linear combination of the normal and shear components of tidal stress that best approximates a constant value when evaluated at the times of Moonquakes from 39 different moonquake clusters. We perform a grid search at each cluster location, computing the stresses resolved onto a suite of possible failure planes, to obtain the best fitting fault orientation at each location. We find that while linear combinations of stresses (and in some cases stress rates) can fit moonquake occurrence at many clusters quite well; for other clusters, the fit is not strongly dependent on plane orientation. This suggests that deep Moonquakes may occur in response to factors other than, or in addition to, tidal stress. Several of our inferences support the hypothesis that deep Moonquakes might be related to transformational faulting, in which shear failure is induced by mineral phase changes at depth. The occurrence of this process would have important implications for the lunar interior.

  • Influence of Earth-Moon orbit geometry on deep moonquake occurrence times
    2008
    Co-Authors: Bruce G. Bills, Renee Bulow, Catherine L. Johnson
    Abstract:

    Introduction: We present a new model for the times of deep focus Moonquakes. This model assumes that, for each deep moonquake cluster, there is a unique linear combination of orbital parameters which is favorable for moonquake occurrence. Because of solar perturbations, the lunar orbit does not exhibit simply periodic behavior. Several deep moonquake clusters exhibit relatively simple, quasi-periodic behavior, with favored periods being either the anomalistic month (27.5545 days), which controls Earth-Moon distance and sub-Earth longitude, or the nodical month (27.2122 days), which controls sub-Earth latitude. Even in these cases, our model performs better, in terms of residual variance (Fisher-Snedecor F ratio), than a purely periodic model, and has the advantage of providing better insight into the cause of the temporal pattern. Background: One of the most intriguing findings of the Apollo Lunar Seismic Experiment [1] was that many of the deep focus events are related to tides raised on the Moon by the Earth [2,3,4]. However, despite considerable past effort [5,6,7,8], many aspects of the deep moonquake situation are still only rather poorly understood. One reason for the continuing difficulty in producing realistic models of the deep moonquake tidal triggering process is that the limited extent and number of the Apollo seismic stations made event location determination difficult. In addition, significant scattering within the Moon made the determination of fault plane orientations even more difficult [9,10]. As a result of these uncertainties in moonquake source parameters, most of the more definitive tests which have been applied to cases of tidal triggering of Earthquakes [11-18] are not feasibly applicable at the Moon. If, for example, the location and orientation of the fault plane at a deep moonquake source were known, it would be a simple matter to project the time-varying tidal stress tensor at that location onto the fault plane, and see whether the resolved shear and normal stresses at event times had repeatable patterns. However, uncertainties in source locations make the tidal stress tensor calculations somewhat uncertain, and the absence of clear seismological evidence for fault plane orientations within the Moon severely limits the critical step of projecting the tensor onto the plane. Given the difficulty in locating and orienting deep moonquake sources, we are motivated to consider an alternative strategy, which depends only upon the very well known relative position and velocity of the Earth, as seen from the Moon. If there were a preferred tidal stress condition, on a deep source fault plane, then we would expect that those conditions would be met only when the tidal stress tensor had the appropriate value. As the tidal stress tensor depends upon both the source (Earth) and receiver (within the Moon) locations, tidal forcing will depend diagnostically upon the relative Earth-Moon position variations. Thus a preferred tidal stress state for triggering of deep Moonquakes implies a preferred combination of position and/or velocity of the tide raising body. The primary objective of the current study is to test the hypothesis that there is, at each deep moonquake cluster, a linear combination of Earth-Moon position and velocity components which is nearly constant at the times of the seismic events at that cluster. Method: Our approach to exploring the connection between orbital parameters and moonquake cluster event times has several steps. The early steps are essentially an empirical orthogonal function (EOF) analysis [19]. We begin by tabulating the values of position and velocity of the Earth, with respect to the Moon, at 1 day intervals over the time span 17 April 1969 to 13 May 1978 (3314 days). The parameters are Earth-Moon distance (re), sub-Earth latitude ( e), sub-Earth longitude (fe), and rates of change of these three. The position values were obtained from the USNO software MICA, and the rates were obtained via differentiation of a cubic-spline interpolation of the position values. It is convenient to use orbital parameters with identical dimensions and comparable dynamic ranges. We thus replace the actual Earth-Moon distance re, with a normalized deviation from the mean value,

  • Temporal and spatial properties of some deep moonquake clusters
    Journal of Geophysical Research, 2007
    Co-Authors: R. C. Bulow, B. G. Bills, Catherine L. Johnson, Peter M. Shearer
    Abstract:

    [1] Using the event search method of Bulow et al. (2005), we have found 503 new deep Moonquakes among the eight largest (in terms of total number) nearside source regions, increasing the number of identified events for each cluster an average of 36% over the existing catalog. These new events provide an improved deep event catalog, with which we explore some temporal and spatial aspects of deep Moonquakes. First, we examine the spectra of moonquake occurrence times at each deep source region, and observe known tidal periodicities, notably those at ∼27 days and 206 days. Application of spectral methods for the analyses of point processes (discrete events) allows us to resolve closely spaced tidal periods not previously seen in moonquake data. Second, we pick seismic phase arrival times from optimized stacks of events from each source region. We use these picks, along with published velocity models, to relocate the nine source regions. Source regions A1 and A18 are the best located, with 95% confidence bounds of less than ±5° in latitude and longitude, and consistent with estimates from different studies. The locations of source regions A8 and A9 are poorly constrained, with uncertainties in latitude of up to ±28° resulting from the absence of clear phase arrivals at station 15. Large trade-offs exist between relocation estimates and choice of velocity model, and the lack of reliable seismic phase arrivals severely affects location error.

Yosio Nakamura - One of the best experts on this subject based on the ideXlab platform.

  • Lunar Seismology: A Data and Instrumentation Review
    Space Science Reviews, 2020
    Co-Authors: Ceri Nunn, Taichi Kawamura, Yosio Nakamura, A. G. Marusiak, Daoyuan Sun, Ludovic Margerin, Mélanie Drilleau, Raphael Garcia, Renee Weber, Mark Wieczorek
    Abstract:

    Several seismic experiments were deployed on the Moon by the astronauts during the Apollo missions. The experiments began in 1969 with Apollo 11, and continued with Apollo 12, 14, 15, 16 and 17. Instruments at Apollo 12, 14, 15, 16 and 17 remained operational until the final transmission in 1977. These remarkable experiments provide a valuable resource. Now is a good time to review this resource, since the InSight mission is returning seismic data from Mars, and seismic missions to the Moon and Europa are in development from different space agencies. We present an overview of the seismic data available from Electronic Supplementary Material The online repository https://doi.org/10.. For each of these, we outline the instrumentation and the data availability. We show examples of the different types of Moonquakes, which are: artificial impacts, meteoroid strikes, shallow quakes (less than 200 km depth) and deep quakes (around 900 km depth). Deep quakes often occur in tight spatial clusters, and their seismic signals can therefore be stacked to improve the signal-to-noise ratio. We provide stacked deep moonquake signals from three independent sources in miniSEED format. We provide an arrival-time catalog compiled from six independent sources, as well as estimates of event time and location where available. We show statistics on the consistency between arrival-time picks from different operators. Moonquakes have a characteristic shape, where the energy rises slowly to a maximum, followed by an even longer decay time. We include a table of the times of arrival of the maximum energy t max and the coda quality factor Q c. Finally, we outline minimum requirements for future lunar missions to the Moon. These requirements are particularly relevant to future missions which intend to share data with other agencies, and set out a path for an International Lunar Network, which can provide simultaneous multi-station observations on the Moon.

  • Lunar Seismology: A Data and Instrumentation Review
    Space Science Reviews, 2020
    Co-Authors: Ceri Nunn, Renee C. Weber, Taichi Kawamura, Yosio Nakamura, Raphaël F. Garcia, A. G. Marusiak, Daoyuan Sun, Ludovic Margerin, Mélanie Drilleau, Mark A. Wieczorek
    Abstract:

    Several seismic experiments were deployed on the Moon by the astronauts during the Apollo missions. The experiments began in 1969 with Apollo 11, and continued with Apollo 12, 14, 15, 16 and 17. Instruments at Apollo 12, 14, 15, 16 and 17 remained operational until the final transmission in 1977. These remarkable experiments provide a valuable resource. Now is a good time to review this resource, since the InSight mission is returning seismic data from Mars, and seismic missions to the Moon and Europa are in development from different space agencies. We present an overview of the seismic data available from four sets of experiments on the Moon: the Passive Seismic Experiments, the Active Seismic Experiments, the Lunar Seismic Profiling Experiment and the Lunar Surface Gravimeter. For each of these, we outline the instrumentation and the data availability. We show examples of the different types of Moonquakes, which are: artificial impacts, meteoroid strikes, shallow quakes (less than 200 km depth) and deep quakes (around 900 km depth). Deep quakes often occur in tight spatial clusters, and their seismic signals can therefore be stacked to improve the signal-to-noise ratio. We provide stacked deep moonquake signals from three independent sources in miniSEED format. We provide an arrival-time catalog compiled from six independent sources, as well as estimates of event time and location where available. We show statistics on the consistency between arrival-time picks from different operators. Moonquakes have a characteristic shape, where the energy rises slowly to a maximum, followed by an even longer decay time. We include a table of the times of arrival of the maximum energy $t_{\max}$ and the coda quality factor $Q_{c}$ . Finally, we outline minimum requirements for future lunar missions to the Moon. These requirements are particularly relevant to future missions which intend to share data with other agencies, and set out a path for an International Lunar Network, which can provide simultaneous multi-station observations on the Moon.

  • The physical mechanisms of deep Moonquakes and intermediate-depth earthquakes: How similar and how different?
    Physics of the Earth and Planetary Interiors, 2009
    Co-Authors: Clifford A Frohlich, Yosio Nakamura
    Abstract:

    We here review the characteristics of deep Moonquakes (DMQ) and conclude that they share many common features with certain categories of intermediate-depth earthquakes, namely, the pressure–temperature conditions where they occur, their occurrence in highly localized nests, their tendency to occur repeatedly at the same or nearly the same location, and their distribution of sizes (b-values). We thus explore various physical mechanisms proposed for earthquakes that might also explain deep Moonquakes. These include the possibility that there are partial melts or fluid phases in the lunar mantle that permit DMQ to occur at pressures where ordinary brittle fracture is not possible, the possibility that stress concentration increases tidal stresses at certain locations where Moonquakes occur repeatedly, and the possibility that DMQ occur at relatively low stresses because rock strength is lowered by a fatigue process induced by the repetitive application of tidal stresses. The similarities between DMQ and terrestrial earthquakes imply that research focusing on the properties of both phenomena may help us understand the physical origins of both.

  • Farside deep Moonquakes and deep interior of the Moon
    Journal of Geophysical Research, 2005
    Co-Authors: Yosio Nakamura
    Abstract:

    [1] An effort to find farside deep Moonquakes among the recently discovered nests of deep Moonquakes has identified about 30 nests that are likely to be on the farside. Although only a few of them are locatable with currently available data and those few provide little new information about the deep interior of the Moon, the inferred distribution of the rest of these nests indicates that either the region of the Moon's deep interior within about 40 degrees from the antipode of the Moon is nearly aseismic or, alternatively, the very deep interior of the Moon severely attenuates or deflects seismic waves. Since this has important bearing on the origin and evolution of the Moon, future missions to the Moon need to be oriented toward resolving this uncertainty. Some limited data favor the attenuation/deflection hypotheses.

  • Spatial Extent of a Deep Moonquake Nest: A Preliminary Report of Reexamination
    2005
    Co-Authors: Yosio Nakamura
    Abstract:

    Deep Moonquakes, occurring at depths about halfway to the center of the Moon, were discovered during the Apollo lunar landing missions, 1969-1972. Their near-monthly occurrence with nearly identical waveforms at any given seismic station suggests that they are strongly influenced by tides, caused by the Earth and the Sun, acting on certain limited regions of the deep lunar interior. However, much about them is unknown, why they are restricted to certain depths and to limited source regions (nests), and what they tell us about the nature of the material and dynamics of the interior of the Moon. A piece of information helpful to decipher their true nature is the spatial extent and distribution of their hypocenters. The occurrence of nearly identical waveforms suggests groups of hypocenters appear in close proximity to one another, but can we tell how closely they are located and how they are distributed? The Apollo PSE (Passive Seismic Experiment) data from all stations of the seismic network were received in real time at a common receiving station on Earth in digital form. This provided extremely high inter-station timing accuracy not achievable for most earthquake data on Earth at that time. We took advantage of this to compute relative locations of waveform-matched events, and concluded that deep moonquake foci in the A1 moonquake nest were concentrated on a nearly horizontal plane of less than 1 km in diameter. This earlier study was based on deep moonquake events visually identified on seismograms. A recent reanalysis of earlier unidentified seismic events fully utilizing the high capability of present-day computers expanded the list of positively identified deep Moonquakes by more than a factor of five. The new list contains many events that are not visually matched in waveforms, yet correlated at a significant level when cross-correlated with a computer. Thus it became imperative to reexamine the spatial distribution of deep moonquake hypocenters including the newly identified events. Additional information is included in the original extended abstract.

Renee C. Weber - One of the best experts on this subject based on the ideXlab platform.

  • Lunar Seismology: A Data and Instrumentation Review
    Space Science Reviews, 2020
    Co-Authors: Ceri Nunn, Renee C. Weber, Taichi Kawamura, Yosio Nakamura, Raphaël F. Garcia, A. G. Marusiak, Daoyuan Sun, Ludovic Margerin, Mélanie Drilleau, Mark A. Wieczorek
    Abstract:

    Several seismic experiments were deployed on the Moon by the astronauts during the Apollo missions. The experiments began in 1969 with Apollo 11, and continued with Apollo 12, 14, 15, 16 and 17. Instruments at Apollo 12, 14, 15, 16 and 17 remained operational until the final transmission in 1977. These remarkable experiments provide a valuable resource. Now is a good time to review this resource, since the InSight mission is returning seismic data from Mars, and seismic missions to the Moon and Europa are in development from different space agencies. We present an overview of the seismic data available from four sets of experiments on the Moon: the Passive Seismic Experiments, the Active Seismic Experiments, the Lunar Seismic Profiling Experiment and the Lunar Surface Gravimeter. For each of these, we outline the instrumentation and the data availability. We show examples of the different types of Moonquakes, which are: artificial impacts, meteoroid strikes, shallow quakes (less than 200 km depth) and deep quakes (around 900 km depth). Deep quakes often occur in tight spatial clusters, and their seismic signals can therefore be stacked to improve the signal-to-noise ratio. We provide stacked deep moonquake signals from three independent sources in miniSEED format. We provide an arrival-time catalog compiled from six independent sources, as well as estimates of event time and location where available. We show statistics on the consistency between arrival-time picks from different operators. Moonquakes have a characteristic shape, where the energy rises slowly to a maximum, followed by an even longer decay time. We include a table of the times of arrival of the maximum energy $t_{\max}$ and the coda quality factor $Q_{c}$ . Finally, we outline minimum requirements for future lunar missions to the Moon. These requirements are particularly relevant to future missions which intend to share data with other agencies, and set out a path for an International Lunar Network, which can provide simultaneous multi-station observations on the Moon.

  • Shallow seismic activity and young thrust faults on the Moon
    Nature Geoscience, 2019
    Co-Authors: Thomas R. Watters, Renee C. Weber, Geoffrey C. Collins, Ian J. Howley, Nicholas C. Schmerr, Catherine L. Johnson
    Abstract:

    Shallow Moonquakes detected at four Apollo landing sites between 1969 and 1977 occurred during maximum stress and in close proximity to young faults, suggesting that the Moon is tectonically active, according to reanalyses of the seismic data and tidal force modelling. The discovery of young thrust faults on the Moon is evidence of recent tectonic activity, but how recent is unknown. Seismometers at four Apollo landing sites recorded 28 shallow Moonquakes between 1969 and 1977. Some of these shallow quakes could be associated with activity on the young faults. However, the epicentre locations of these quakes are poorly constrained. Here we present more-accurate estimates of the epicentre locations, based on an algorithm for sparse seismic networks. We found that the epicentres of eight near-surface quakes fall within 30 km of a fault scarp, the distance of the expected strong ground shaking. From an analysis of the timing of these eight events, we found that six occurred when the Moon was less than 15,000 km from the apogee distance. Analytical modelling of tidal forces that contribute to the current lunar stress state indicates that seven near-apogee events within 60 km of a fault scarp occur at or near the time of peak compressional stresses, when fault slip events are most likely. We conclude that the proximity of Moonquakes to the young thrust faults together with evidence of regolith disturbance and boulder movements on and near the fault scarps strongly suggest the Moon is tectonically active.

  • Recovery of Deep Moonquake Focal Mechanisms
    2012
    Co-Authors: Renee C. Weber, Martin Knapmeyer
    Abstract:

    Deep Moonquakes are clustered not only in space but also in time: their recurrence times correspond to the durations of the anomalistic and draconic months, with some clusters preferring one of the two periods, while others are active with both periods. A key constraint for the understanding of the connection between the orbital motion of the Moon and its seismic activity is the focal mechanism: the orientation of the fault surface on which failure occurs during the quake. Due to the small aperture of the Apollo seismic network and the strong scattering of seismic waves within the lunar crust, the evaluation of P wave first motions to constrain the strike and dip of the fault planes is not feasible. Instead we evaluate the amplitude ratios of P and S waves. Seismograms are rotated into the P-SV-SH coordinate frame and amplitudes are determined as averages over short time windows after the arrival to reduce the impact of the scattering coda, which is independent of the source orientation. We allow for reversals of the fault motion, as observed for some clusters in previous studies, by taking into account the absolute amplitude only, without sign. An empirical site correction factor is applied to correct for amplitude distortions in the crust. We construct ensembles of fault plane solutions using an exhaustive grid search by accepting all orientations that reproduce the measured amplitude ratios within the observed standard deviations. Since all events of a given cluster are supposed to share the same fault plane, the combination of the individual inversion results further constrains the orientation. We evaluate 106 events from 25 different moonquake clusters. The most active cluster A001 contributes 37 events, while others contribute 1 to 9 events per cluster. Comparison of fault orientations with the variation of the tidal stress results in preferred orientations.

  • Deep Moonquake Focal Mechanisms: Recovery and Implications
    2011
    Co-Authors: Martin Knapmeyer, Renee C. Weber
    Abstract:

    A defining characteristic of deep Moonquakes is their tendency to occur with tidal periodicity, prompting previous studies to infer that they are related to the buildup and release of tidal stress within the Moon. In studies of tidal forcing, a key constraint is the focal mechanism: the fault parameters describing the type of failure Moonquakes represent. The quality of the lunar seismic data and the limited source/receiver geometries of the Apollo seismic network prohibit the determination of deep moonquake fault parameters using first-motion polarities, as is typically done in terrestrial seismology. Without being able to resolve tidal stress onto a known failure plane, we can examine only gross qualities of the tidal stress tensor with respect to moonquake occurrence, so we cannot fully address the role of tidal stress in moonquake generation. We will examine the extent to which shear (S) and compression (P) wave amplitude ratios can constrain moonquake fault geometry by determining whether, for a given cluster, there exists a focal mechanism that can produce a radiation pattern consistent with the amplitudes measured by the Apollo instruments. Amplitudes are read in the ray coordinate frame, directly from seismograms for which the P and S arrivals are clearly identifiable on all long-period channels of the four Apollo stations. We apply an empirical station correction to account for site effects and the differences between P- and S-wave attenuation. Instead of focusing on the best fitting solution only, we formulate the inverse problem using a falsification criterion: all source orientations that do not reproduce the observed SV/P ratios within an error margin derived from the uncertainty of amplitude readings are rejected. All others are accepted as possible solutions. The inversion is carried out using an exhaustive grid search on a regular grid with predefined step size, encompassing all possible combinations of strike, dip and slip. To assess the sensitivity of the inversion for the uncertainty of the lunar interior structure, we carry out repeated inversions with different velocity structures. Our data set consist of a total of 106 events from 25 deep moonquake clusters. The largest contribution of 37 events originates from the most active cluster, A001, while other clusters are represented by 1 to 9 events. Since the definition of a cluster implies that all events share the same source orientation, a comparison of the inversion results of all events from one cluster will reduce ambiguities of the inversion. Once we obtain a suite of fault parameters for a given source, we can attempt to further constrain the focal mechanism with refined analyses of tidal stresses and predictions based on synthetic seismograms.

  • Imaging the Moon's Core with Seismology
    2011
    Co-Authors: Renee C. Weber, Pei-ying Patty Lin, Edward J. Garnero, Quetin C. Williams, Philippe Lognonné
    Abstract:

    Constraining the structure of the lunar core is necessary to improve our understanding of the present-day thermal structure of the interior and the history of a lunar dynamo, as well as the origin and thermal and compositional evolution of the Moon. We analyze Apollo deep moonquake seismograms using terrestrial array processing methods to search for the presence of reflected and converted energy from the lunar core. Although moonquake fault parameters are not constrained, we first explore a suite of theoretical focal spheres to verify that fault planes exist that can produce favorable core reflection amplitudes relative to direct up-going energy at the Apollo stations. Beginning with stacks of event seismograms from the known distribution of deep moonquake clusters, we apply a polarization filter to account for the effects of seismic scattering that (a) partitions energy away from expected components of ground motion, and (b) obscures all but the main P- and S-wave arrivals. The filtered traces are then shifted to the predicted arrival time of a core phase (e.g. PcP) and stacked to enhance subtle arrivals associated with the Moon s core. This combination of filtering and array processing is well suited for detecting deep lunar seismic reflections, since we do not expect scattered wave energy from near surface (or deeper) structure recorded at varying epicentral distances and stations from varying Moonquakes at varying depths to stack coherently. Our results indicate the presence of a solid inner and fluid outer core, overlain by a partial-melt-containing boundary layer (Table 1). These layers are consistently observed among stacks from four classes of reflections: P-to-P, S-to-P, P-to-S, and S-to-S, and are consistent with current indirect geophysical estimates of core and deep mantle properties, including mass, moment of inertia, lunar laser ranging, and electromagnetic induction. Future refinements are expected following the successful launch of the GRAIL lunar orbiter and SELENE 2 lunar lander missions.

Gary Daines - One of the best experts on this subject based on the ideXlab platform.

Hiroshi Ishikawa - One of the best experts on this subject based on the ideXlab platform.

  • 3PGCIC - SOM-Based Visualization for Classifying Large-Scale Sensing Data of Moonquakes
    2013 Eighth International Conference on P2P Parallel Grid Cloud and Internet Computing, 2013
    Co-Authors: Yasumichi Goto, Ryuhei Yamada, Yukio Yamamoto, Shohei Yokoyama, Hiroshi Ishikawa
    Abstract:

    Large-scale seismic data were obtained from seismometers located on the Moon by the NASA Apollo missions from 1969 to 1977. According to previous analysis of the lunar seismic data, we found that deep Moonquakes occur periodically from identical sources at a depth of about 700 to 1200km. The deep Moonquakes occurred from identical sources have high similarities among each waveform. This similarity is important to classify the sources and investigate the generation mechanism of Moonquakes. From the reason, classification of Moonquakes has been processed. We, therefore, develop the web system for visualizing Moonquakes considering the waveform similarity to progress study of moonquake classification. Our system maps Moonquakes data to two dimensional output space using Self-Organizing Map (SOM). We embed Hadoop in the back-end system to apply SOM to enormous Moonquakes data. In this paper, to select a feature for SOM, we evaluate several features based on classified data. Using selected feature, we perform SOM to moonquake data and discuss its result.

  • som based visualization for classifying large scale sensing data of Moonquakes
    2013 Eighth International Conference on P2P Parallel Grid Cloud and Internet Computing, 2013
    Co-Authors: Yasumichi Goto, Ryuhei Yamada, Yukio Yamamoto, Shohei Yokoyama, Hiroshi Ishikawa
    Abstract:

    Large-scale seismic data were obtained from seismometers located on the Moon by the NASA Apollo missions from 1969 to 1977. According to previous analysis of the lunar seismic data, we found that deep Moonquakes occur periodically from identical sources at a depth of about 700 to 1200km. The deep Moonquakes occurred from identical sources have high similarities among each waveform. This similarity is important to classify the sources and investigate the generation mechanism of Moonquakes. From the reason, classification of Moonquakes has been processed. We, therefore, develop the web system for visualizing Moonquakes considering the waveform similarity to progress study of moonquake classification. Our system maps Moonquakes data to two dimensional output space using Self-Organizing Map (SOM). We embed Hadoop in the back-end system to apply SOM to enormous Moonquakes data. In this paper, to select a feature for SOM, we evaluate several features based on classified data. Using selected feature, we perform SOM to moonquake data and discuss its result.