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The Apollo astronauts deployed seismic experiments on the nearside of the Moon between 1969 and 1972. Five stations collected passive seismic data. Apollo 11 operated for around 20 days, and stations 12, 14, 15, and 16 operated nearly continuously from their installation until 1977. Seismic data were collected and digitized on the Moon and transmitted to Earth. The data were recorded on magnetic reel-to-reel tapes, with timestamps representing the signal reception time on Earth. The taped data have been widely used for many applications and have previously been shared in various formats. The data have slightly varying sampling rates, due to random fluctuations of the data sampler and also its sensitivity to the significant temperature variations on the Moon’s surface. Additionally, there were timing errors. Previously shared versions of the Apollo data were affected by these problems. We have reimported the passive data to SEED (Standard for the Exchange of Earthquake Data) format, and we make these data available via Incorporated Research Institutions for Seismology and the Planetary Data System. We have cleaned the timestamp series to reduce incorrectly recorded timestamps. The archive includes five tracks: three components of the mid-period seismometers, one short-period component, and a time track containing the timestamps. The seismic data are provided unprocessed in their raw format, and we provide instrument response files. We hope that the new archive will make it easier for a new generation of seismologists to use these data to learn more about the structure of the Moon.

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. ISSN:1572-9672 ISSN:0038-6308

To get started, read DataPaper_ElectronicSup1.docx. This repository is a collection of resources for lunar seismology, including: S1: Location Parameters S2 - Deep Moonquake Stacks S3 - Lunar Catalog from Various Sources S4 - Extensive Lunar Catalog from Nakamura et al. 1981 and updates S5 - Attenuation Parameters from Gillet et al. (2017) S6 - Low-Level Requirements for Future Seismic Missions to the Moon S7 - Jupyter Notebook to plot the transfer functions S8 - Block Diagrams S9 - Artificial Impacts S10 - Current Data Availability S11 - Response Files, Replaced ImpactParameters.xlsx with ImpactParameters.csv which is easier to import and use. Also corrected an error in the date of the Apollo 15 Lunar Module (A15/LM) impact.

The Apollo Heat Flow Experiment (HFE) was conducted at landing sites 15 and 17. On Apollo 15, surface and subsurface temperatures were monitored from July 1971 to January 1977. On Apollo 17, monitoring took place from December 1972 to September 1977. The investigators involved in the HFE examined and archived only data from the time of deployment to December 1974. The present authors recovered and restored major portions of the previously un-archived HFE data from January 1975 through September 1977. The HFE investigators noted that temperature of the regolith well below the reach of insolation cycles (approx. 1 m) rose gradually through December 1974 at both sites. The restored data showed that the subsurface warming continued until the end of observations in 1977. Simultaneously, the thermal gradient decreased, because the warming was more pronounced at shallower depths. The present study has examined potential causes for the warming. Recently acquired images of the Lunar Reconnaissance Orbiter Camera over the two landing sites show that the regolith on the paths of the astronauts turned darker, lowering the albedo. We suggest that, as a result of the astronauts' activities, solar heat intake by the regolith increased slightly on average, and that resulted in the observed warming. Simple analytical heat conduction models with constant regolith thermal properties can show that an abrupt increase in surface temperature of 1.6 K to 3.5 K at the time of probe deployment best duplicate the magnitude and the timing of the observed subsurface warming's at both Apollo sites.

A data product has been generated and archived on the NASA Planetary Data System (Geosciences Node), which presents the seismometer readings of Viking Lander 2 in an easy-to-access form, for both the raw (“high rate”) waveform records and the compressed (“event mode”) amplitude and frequency records. In addition to the records themselves, a separate summary file for each instrument mode lists key statistics of each record together with the meteorological measurements made closest in time to the seismic record. This juxtaposition facilitates correlation of the seismometer instrument response to different meteorological conditions, or the selection of seismic data during which wind disturbances can be expected to be small. We summarize data quality issues and also discuss lander-generated seismic signals, due to operation of the sampling arm or other systems, which may be of interest for prospective missions to other bodies. We review wind-seismic correlation, the “Martian solar day (sol) 80” candidate seismic event, and identify the seismic signature of a probable dust devil vortex on sol 482 : the seismometer data allow an estimate of the peak wind, occurring between coarsely spaced meteorology measurements. We present code to generate the plots in this paper to illustrate use of the data product.

The InSight mission on Mars is currently providing us with the first seismic data from a planetary body other than our own Earth since the 1970s. Past efforts will inform this next chapter in planetary seismology.

International audience; An international team of researchers gathered, with the support of the Interna-tional Space Science Institute (ISSI), (1) to review seismological investigations of the lunarinterior from the Apollo-era and up until the present and (2) to re-assess our level of knowl-edge and uncertainty on the interior structure of the Moon. A companion paper (Nunn et al.in Space Sci. Rev., submitted) reviews and discusses the Apollo lunar seismic data with theaim of creating a new reference seismic data set for future use by the community. In thisstudy, we first review information pertinent to the interior of the Moon that has becomeavailable since the Apollo lunar landings, particularly in the past ten years, from orbitingspacecraft, continuing measurements, modeling studies, and laboratory experiments. Fol-lowing this, we discuss and compare a set of recent published models of the lunar interior,including a detailed review of attenuation and scattering properties of the Moon. Commonfeatures and discrepancies between models and moonquake locations provide a first esti-mate of the error bars on the various seismic parameters. Eventually, to assess the influenceof model parameterisation and error propagation on inverted seismic velocity models, aninversion test is presented where three different parameterisations are considered. For thispurpose, we employ the travel time data set gathered in our companion paper (Nunn et al. inSpace Sci. Rev., submitted). The error bars of the inverted seismic velocity models demon-strate that the Apollo lunar seismic data mainly constrain the upper- and mid-mantle struc-ture to a depth of ∼1200 km. While variable, there is some indication for an upper mantlelow-velocity zone (depth range 100–250 km), which is compatible with a temperature gradi-◦ent around 1.7 C/km. This upper mantle thermal gradient could be related to the presenceof the thermally anomalous region known as the Procellarum Kreep Terrane, which containsa large amount of heat producing elements.

Fourteen types of geophysical instruments deployed at the Apollo 12, 14, 15, 16, and 17 sites by the astronauts for long-term observation were collectively called the Apollo Lunar Surface Experiments Package (ALSEP). These instruments were active from the times of their deployment (November 1969–December 1972) to September 1977. At the conclusion of the experiments, the raw instrument data received from the Moon prior to March 1976 were left unarchived. Portions of the data processed by the principal investigators (PIs) of these experiments had been archived at the NASA Space Science Data Coordinated Archive (NSSDCA) in various formats. The unarchived data, residing then on open-reel magnetic tapes, became lost in the decades since, along with much of the metadata (the supporting documents for these data). We have recently recovered 440 of the previously lost tapes, containing raw ALSEP instrument data from April through June of 1975. Here we describe the data extracted from these tapes and summarize the data products generated for archiving at the NASA Planetary Data System (PDS) and NSSDCA, along with their historical narrative. In addition, we have reformatted many of the datasets delivered to NSSDCA by the PIs in the 1970s for archiving at the PDS. Finally, we have compiled an online searchable repository of ALSEP-related documents by optically scanning tens of thousands of pages of them kept at the Lunar and Planetary Institute in Texas.

Enigmatic lunar seismograms recorded during the Apollo 17 mission in 1972 have so far precluded the identification of shear-wave arrivals and hence the construction of a comprehensive elastic model of the shallow lunar subsurface. Here, for the first time, we extract shear-wave information from the Apollo active-seismic data using a novel waveform analysis technique based on spatial seismic wavefield gradients. The star-like recording geometry of the active seismic experiment lends itself surprisingly well to compute spatial wavefield gradients and rotational ground motion as a function of time. These observables, which are new to seismic exploration in general, allowed us to identify shear waves in the complex lunar seismograms, and to derive a new model of seismic compressional and shear-wave velocities in the shallow lunar crust, critical to understand its lithology and constitution, and its impact on other geophysical investigations of the Moon's deep interior.

Strange quark matter made of up, down and strange quarks has been postulated by Witten [E. Witten, Phys. Rev D 30 (1984) 279]. Strange quark matter would be nearly charge neutral and would have density of nuclear matter (1014 gm/cm3). Witten also suggested that nuggets of strange quark matter, or strange quark nuggets (SQNs), could have formed shortly after the Big Bang, and that they would be viable candidates for cold dark matter. As suggested by de Rujula and Glashow [A. de Rujula and S. Glashow, Nature 312 (1984) 734], an SQN may pass through a celestial body releasing detectable seismic energy along a straight line. The Moon, being much quieter seismically than the Earth, would be a favorable place to search for such events. We review previous searches for SQNs to illustrate the parameter space explored by using the Moon as a low-noise detector of SQNs. We also discuss possible detection schemes using a single seismometer, and using an International Lunar Seismic Network.

Reanalysis of lunar seismic data collected during the Apollo program indicates that 23 of the 28 rare events known as high-frequency teleseismic (HFT) events or shallow moonquakes occurred during one-half of the sidereal month when the seismic network on the Moon's near side faced approximately towards right ascension of 12 h on the celestial sphere. Statistical analysis demonstrates that there is about a 1% probability that this pattern would occur by chance. An alternate possibility is that high-energy objects from a fixed source outside the Solar System trigger or even cause the HFT events.

Joint interpretation of disparate geophysical datasets can be a powerful tool in deriving meaningful subsurface geologic models. Here we describe a method for joint inversion of first arrival travel-time and gravity data with application to field data from a geologically complex subduction zone. As both tomographic and gravity inversions are prone to non-uniqueness, incorporation of prior information in the model description is crucial to the success of such algorithms. We employ a layer-based model description, in which interfaces (which may also be called iso-velocity lines) are defined by a summation of arc-tangent functions. Arc-tangent functions are highly flexible in mapping smooth interfaces as well as the nearly discontinuous changes in depth of an interface. Within each layer, the velocity is assumed to vary linearly with depth at each surface location. Because of the non-uniqueness of the gravity inversion, we use prior knowledge to relate the velocity to density values. In our application here, the density is related to the velocity using a fourth-order polynomial whose coefficients are assumed to be known. The nonlinear optimization problem is solved by a very fast simulated annealing (VFSA) technique. At each iteration, travel times are generated by the solution of the Eikonal equation while the gravity anomalies are computed using a standard formula. The objective function consists of two parts: one measures the misfit in travel time and the other measures the misfit of gravity anomalies. We applied our technique to field data collected over the Ryukyu subduction zone offshore Taiwan during an ocean bottom seismometer (OBS) experiment (called TAICRUST) conducted in the year 1995. Application to one NS and one EW trending line resulted in acceptable fit of both travel-time and gravity data. The resulting models are helpful in the interpretation of the local geology.

We have used combined onshore and offshore wide-angle seismic data sets to model the velocity structure of the Taiwan arc–continent collision along three cross-island transects. Although Taiwan is well known as a collisional orogen, relatively few data have been collected that reveal the deeper structure resulting from this lithospheric-scale process. Our southern transect crosses the Hengchun Peninsula of southernmost Taiwan and demonstrates characteristics of incipient collision. Here, 11-km-thick, transitional crust of the Eurasian plate (EUP) subducts beneath a large, rapidly growing accretionary prism. This prism also overrides the N. Luzon forearc to the east as it grows. Just west of the arc axis there is an abrupt discontinuity in the forearc velocity structure. Because this break is accompanied by intense seismicity, we interpret that the forearc block is being detached from the N. Luzon arc and Philippine Sea plate (PSP) at this point. Our middle transect illustrates the structure of the developing collision. Steep and overturned velocity contours indicate probable large-scale thrust boundaries across the orogen. The leading edge of the coherent PSP appears to extend to beneath the east coast of Taiwan. Deformation of the PSP is largely limited to the remnant N. Luzon arc with no evidence of crustal thickening to the east in the Huatung basin. Our northern transect illustrates slab–continent collision—the continuing collision of the PSP and EUP as the PSP subducts. The collisional contact is below ∼20 km depths along this transect NE of Hualien. This transect shows elements of the transition from arc–continent collision to Ryukyu arc subduction. Both of our models across the Central Range suggest that the Paleozoic to Mesozoic basement rocks there may have been emplaced as thick, coherent thrust sheets. This suggests a process of partial continental subduction followed by intra-crustal detachment and buoyancy-aided exhumation. Although our models provide previously unknown structural information about the Taiwan orogen, our data do not define the deepest orogenic structure nor the structure of western Taiwan. Additional seismic (active and passive), geologic, and geodynamic modeling work must be done to fully define the structure, the active deformation zones, and the key geodynamic process of the Taiwan arc–continent collision.

A new computer search of the Apollo lunar seismic data set for identification of deep moonquakes using a combination of waveform cross-correlation and single-link cluster analysis has increased the number of positively identified deep moonquakes by more than a factor of five, from the previous 1360 to 7245. At least 88 new deep moonquake source regions (nests) have been discovered, while some source regions previously identified as separate entities are now determined to be identical, reducing the number of previously known source regions from 108 to 77. The newly identified deep moonquakes and their relationships to each other are likely to revise our understanding of their spatial and temporal distributions.

We present an in situ evaluation of the response of seafloor sediments to passive dynamic loads. Horizontal-to-vertical (H/V) spectral ratios are used to characterize local sediment response, and 1D wave propagation modeling is used to estimate soil properties and theoretical amplification factors of shallow sediment layers. Horizontal amplitudes increased by an order of magnitude at 0.35 Hz and by at least 2 orders of magnitude at 1.9 Hz relative to the vertical amplitude. A 50-m-thick soil system parameterized as three solid layers resting over a half-space with a water layer at the top produces theoretical H/V spectral ratios that are largely consistent with the observed H/V spectral ratios. Our modeling results were consistent between earthquake and background noise records. Modeling H/V spectral ratios of noise data recorded by a three-component broadband ocean-bottom seismograph (BBOBS) offers a fast and inexpensive method for site investigation in deep water with the potential of in situ seafloor sediment characterization, as well as local site effect studies for foundations (30-100 m) and pipelines (2-5 m) in deep water. One need not supply an active source or wait for an appropriate earthquake, and the BBOBS is small, inexpensive, and autonomous once deployed. Manuscript received 23 October 2001.

We present the results of a wide-angle seismic survey conducted over the Chicxulub impact crater. Profile Chicx-A/A1 is a chord across the offshore portion of the crater, and Chicx-B/F is an onshore-offshore profile through the center of the crater. We use travel times recorded by 32 ocean bottom seismograph and 19 land-based receivers to model the crustal structure of the crater. The primary feature in the shallow velocity structure is a low-velocity Tertiary basin, the edge of which correlates with a steep gravity gradient in some regions of our survey. Directly beneath the Tertiary basin at the center of the crater is a region of relatively low velocities and densities that is interpreted as a unit of melt rocks (either suevite breccias with isolated melt pods or suevite breccias overlying a coherent melt sheet). This unit has a thickness of ∼1 km and a diameter of ∼100 km. Central uplift with a diameter of 40–60 km is observed on Chicx-B/F. A lower limit on the vertical extent of uplift is 9 km. Shallow basement is also observed along the northwest portion of Chicx-B/F, associated with a prominent northwest trending high in the gravity field. Superimposed on a regional trend is Moho uplift of ∼1 km near the center of the Chicx-A/A1 profile, with adjacent Moho deepening of ∼1.25–1.5 km. The Moho topography may be related to deformation processes associated with the formation of the outer ring or to the excavation and collapse of the transient cavity.

A wide-angle seismic survey, combining ocean-bottom seismometers (OBS) and multi-channel seismic (MCS) profiling, was implemented in the southwestern Ryukyu subduction zone during August and September 1995. In this paper, we present the data analysis of eight OBSs and the corresponding MCS line along profile EW9509-1 from this experiment. Seismic data modeling includes identification of refracted and reflected arrivals, initial model building from velocity analysis of the MCS data, and simultaneous and layer-stripping inversions of the OBS and MCS arrivals. The velocity-interface structure constructed along profile EW9509-1 shows that the northward subduction of the Philippine Sea Plate has resulted in a northward thickening of the sediments of the Ryukyu Trench and the Yaeyama accretionary wedge north of the trench. The boundary between the subducting oceanic crust and the overriding continental crust (represented by a velocity contour of 6.75 km/s) and a sudden increase of the subducting angle (from 5 degrees to 25 degrees) are well imaged below the Nanao Basin. Furthermore, velocity undulation and interface variation are found within the upper crust of the Ryukyu Arc. Therefore, the strongest compression due to subduction and a break-off of the slab may have occurred and induced the high seismicity in the forearc region.

In March and April 1995 a cooperative German, Costa Rican, and United States research team recorded onshore-offshore seismic data sets along the Pacific margin of Costa Rica using the R/V Ewing. Off the Nicoya Peninsula we used a linear array of ocean bottom seismometers and hydrophones (OBS/H) with onshore seismometers extending across much of the isthmus. In the central area we deployed an OBS/H areal array consisting of 30 instruments over a 9 km by 35-km area and had land stations on the Nicoya Peninsula adjacent to this marine array and also extending northeast on the main Costa Rican landmass. Our goal in these experiments was to determine the crustal velocity structure along different portions of this convergent margin and to use the dense instrument deployments to create migrated reflection images of the plate boundary zone and the subducting Cocos Plate. Our specific goal in the central area was to determine whether a subducted seamount is present at the location of the 1990, M 7 earthquake off the Nicoya Peninsula and can thus be linked to its nucleation. Subsequently we have processed the data to improve reflection signals, used the data to calculate crustal velocity models, and developed several wide-aperture migration techniques, based on a Kirchhoff algorithm, to produce reflection images. Along the northern transect we used the ocean bottom data to construct a detailed crustal velocity model, but reflections from the plate boundary and top and bottom of the subducting Cocos plate are difficult to identify and have so far produced poor images. In contrast, the land stations along this same transect recorded clear reflections from the top of the subducting plate or plate boundary, within the seismogenic zone, and we have constructed a clear image from this reflector beneath the Nicoya shelf. Data from the 3-D seismic experiment suffer from high-amplitude, coherent noise (arrivals other than reflections), and we have tried many techniques to enhance the signal to noise ratio of reflected arrivals. Due to the noise, an apparent lack of strong reflections from the plate boundary zone, and probable structural complexity, the resulting 3-D images only poorly resolve the top of the subducting Cocos Plate. The images are not able to provide compelling evidence of whether there is a subducting seamount at the 1990 earthquake hypocenter. Our results do show that OBS surveys are capable of creating images of the plate boundary zone and the subducting plate well into the seismogenic zone if coherent reflections are recorded at 1.8 km instrument spacing (2-D) and 5 km inline by 1 km crossline spacing for 3-D acquisition. However, due to typical high amplitude coherent noise, imaging results may be poorer than expected, especially in unfavorable geologic settings such as our 3-D survey area. More effective noise reduction in acquisition, possibly with the use of vertical hydrophone arrays, and in processing, with advanced multiple removal and possibly depth filtering, is required to achieve the desired detailed images of the seismogenic plate boundary zone.

The Chicxulub impact in Mexico has been linked to the mass extinction of species at the end of the Cretaceous period. From seismic data collected across the offshore portion of the impact crater, the diameter of the transient cavity is determined to be about 100 km. This parameter is critical for constraining impact-related effects on the Cretaceous environment, with previous estimates of the cavity diameter spanning an order of magnitude in impact energy. The offshore seismic data indicate that the Chicxulub crater has a multi-ring basin morphology, similar to large impact structures observed on other planets, such as Venus.

Data collected by 18 ocean bottom receivers for a seismic line shot at both 50-m (∼24 s shot interval) and 125-m (∼58 s shot interval) shot spacing provide a direct field comparison of the effect of shot interval on marine wide-angle seismic data. Our results indicate that both shot spacings produce high-quality refraction data in shallow water (

Seismic profiling data indicate that the thickness of an accreted oceanic terrane of Paleocene and early Eocene age, which forms the basement of much of the forearc beneath western Oregon and Washington, varies by approximately a factor of 4 along the strike of the Cascadia subduction zone. Beneath the Oregon Coast Range, the accreted terrane is 25 to 35 kilometers thick, whereas offshore Vancouver Island it is about 6 kilometers thick. These variations are correlated with variations in arc magmatism, forearc seismicity, and long-term forearc deformation. It is suggested that the strength of the forearc crust increases as the thickness of the accreted terrane increases and that the geometry of the seaward edge of this terrane influences deformation within the subduction complex and controls the amount of sediment that is deeply subducted.

[1] It has recently been discovered that the Apollo 17 Lunar Module (LM) impact data from the Lunar Seismic Profiling Experiment (LSPE) had a serious timing problem. Correcting this problem changes the lunar near-surface seismic velocity structure significantly from the structural models reported in the earlier publications, extending a low-velocity (Vp∼1 km/s) layer down to a 3 km depth or deeper.

A difference is noted between meteoroids whose masses lie above and below 1 kg in temporal meteoroid-impact clusterings detected by the Apollo lunar seismic network; while the former exhibit little temporal clustering, small ones show strong clusterings identifiable with terrestrial meteor showers. This finding suggests a different type and origin for the two meteoroid sizes; the small may be primarily cometary, while the large may derive from near-earth asteroids and short-period comets. It is speculated that the June, 1975, and January, 1977 swarms of large meteoroids may contain high-density meteoritic objects interpretable as meteorite streams.

We have reconfigured the Texas digital ocean bottom seismograph (OBS) to operate in a triggered mode and record regional earthquake signals. This paper reports the results of a deployment program designed to test these digital OBS, by moni toring earthquake activity in and near the trench in southern Vanuatu (formerly, the New Hebrides). We successfully recorded hundreds of earthquakes, including 133 located regional earth quakes recorded by three or more stations. We also report J-B residuals for 21 earthquakes reported and located by the ISC. Fourier analysis of seismograms from regional earthquakes suggest that the frequencies of spectral peaks at any station were nearly the same for large, small, nearby, and distant events. However, we obtained very disparate frequencies when we analyzed seismograms for the same earthquake recorded at different stations. The most plausible interpretation is that spectral peaks do not depend on the characteristics of the earthquake source, but instead on site characteristics, or, more specifically, on the coupling of the instrument to the seafloor. To record reliable spectral data, we need to overcome this problem.

[1] We present multichannel seismic reflection and ocean bottom seismometer reflection/refraction data from ISE-9, a margin-parallel, north–south oriented profile ∼200 km west of the Portuguese coast. ISE-9 images the boundary between two distinct segments of the Iberia nonvolcanic rifted margin: Galicia Bank (GB) and the Southern Iberia Abyssal Plain (SIAP). The bathymetric contrast between GB (2 km depth) and SIAP (4–5 km depth) spans only 25 km. The crustal thickness transition, however, spans 137 km, from 13–18 km thick beneath GB to

International audience; By correlating seismic noise recorded by four sensors placed on the Moon during the Apollo 17 mission, we have retrieved a well-defined dispersed Rayleigh wave pulse. Inversion of its group velocity provides new constraints on the lunar subsurface structure. The estimated ”signal-to-noise” ratio (SNR) of the retrieved Rayleigh wavetrain is strongly dependent on solar illumination, effectively making solar heating a source of seismic noise on the Moon. This result suggests that in future planetary missions it is feasible to extract information on the internal structure of extraterrestrial objects by correlating seismic noise even when natural quakes are absent.

[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.

We determine S-wave crustal velocity structure of the Sigsbee abyssal plain in the Gulf of the Mexico, using multicomponent ocean bottom seismometer data. We first construct a 2-D P-wave velocity model by applying a raybased travel-time inversion to the vertical component data. Then, we make an attempt to identify in the radial component records the events associated with P-S mode conversion. Using iterative forward modeling, we constrain S-wave velocities of the layers identified in the P-wave model. We are able to identify the mode-converted events with high confidence, because of the relatively simple geologic structure of the area. Vp/Vs values of the sedimentary layers and their relationship with Vp is indicative of lithologic change with depth: poorly consolidated shale at the top, compacted shale in the middle, and carbonates at the bottom.

We used travel times recorded by 23 ocean bottom seismograph (OBS) receivers to model crustal structure of the Chicxulub impact crater. The OBSs were located along Chicx-A/A1, a deep reflection profile extending as a chord across the offshore portion of the Chicxulub structure. A tomographic inversion of crustal refractions was used to produce the upper crustal structure. The prominent feature in the shallow velocity structure is the low velocities associated with the Tertiary basin. The low velocity section is thickest near the center of the crater, and thins on the flanks. High velocities observed near the surface along several portions of the crater flanks may represent the widespread presence of reefal buildups at the margins of the Tertiary basin. Negative velocity anomalies observed beneath the Tertiary basin within the collapsed transient cavity are interpreted as melt rocks. The largest negative anomaly is located near the center of Chicx-A/A1 (~26 km from the interpreted center of the crater), and extends laterally 50 km. The depth to the top of this anomaly is about 1 km; its average thickness is 1.3 km. Two smaller anomalies are located near the eastern and western margins of the collapsed transient cavity. The average thickness of these three negative velocity anomalies, when averaged over the width of the collapsed transient cavity, is 1 km. Christeson, G. L., Buffler, R. T., and Nakamura, Y., 1999, Upper crustal structure of the Chicxulub impact crater from wide-angle ocean bottom seismograph data, in Dressler, B. O., and Sharpton, V. L., eds., Large Meteorite Impacts and Planetary Evolution II: Boulder, Colorado, Geological Society of America Special Paper 339

The ongoing orogeny in Taiwan is a result of the collision of the PhilippineSea and the Eurasian plates.While the structure of the continentalcrust on the Eurasian plate(EP)is now mostly known,that of the oceaniccrust on the Philippine Sea plate(PSP)is not well mapped.Using offshore-onshore refraction data,collected during the R/V Ewing cruise of 1995,weinvestigate the nature of the transition between the EP and the PSP in thevicinity of the southern Coastal Range of Taiwan.The data were producedby the air-gun array of the R/V Ewing along a WNW-ESE trending line offthe coast of central Taiwan(MCS/OBS line 23).The refracted P waveswere collected by 19 RefTek recorders with L-28 sensors placed along thesouthern cross-island highway of Taiwan,which is the onshore extension ofline 23.Because of high noise levels in the Coastal Plain,we were only ableto retrieve usable data from 11 stations located from the east coast throughthe Central Range.We performed forward modeling of the first arrivingwaves at these stations;our strategy was to search for the simplest modelthat fitted all the data.Our results indicate that the crust thickens graduallytoward Taiwan,from about 9-12km thick in the Huatung basin to 15-18km thick off the eastern coast of Taiwan,with a 4-8 degree dip of theMoho.Continuing westward,the crust thickens more rapidly to 27-32kmthick under the east coast of Taiwan,with a 26-32 degree dip of the Moho.

本研究は, 屋外に設置される彫刻作品やそれに類する作品を「オブジェ」と総称し, その設置の際に考慮されるべき意味的調和の理念を構築することを大きな目的とする。この目的のため, アンケート調査を実施し, その結果を意味関連図に整理することによって, 意味関連の型式を抽出し, オブジェ設置の際の関連図の有川性を呈示した。

The meteoroid impact-seismic activity data recorded by the Apollo lunar seismic network is examined. The study investigates the difference in temporal distribution between large and small impacts, clustering of impacts in a two-dimensional space of the time of the year and the time of the month, and the relationship of these observations with terrestrial observations. Several distinct families of meteoroids impacting the moon are identified. Most meteoroids producing small impact-seismic events, including ones associated with cometary showers, appear to approach from retrograde heliocentric orbits. In contrast, most meteoroids associated with large impact-seismic events appear to approach from prograde orbits; the observation is consistent with a hypothesis that many of them represent stony asteroidal material. It is suggested that the previously reported discrepancy between lunar and terrestrial meteoroid-flux estimates may be due to the differences in lunar and terrestrial detection efficiency among various families of meteoroids.

The Apollo lunar seismic station network gathered data continuously at a rate of 3 x 10 to the 8th bits per day for nearly eight years until termination in September, 1977. The data were processed and analyzed using a PDP-15 minicomputer. On average, 1500 long-period seismic events were detected yearly. Automatic event detection and identification schemes proved unsuccessful because of occasional high noise levels and, above all, the risk of overlooking unusual natural events. The processing procedures which were finally chosen consist of plotting all the data on a compressed time scale, visually picking events from the plots, transferring event data to separate sets of tapes and performing detailed analyses using the latter. Many problems remain, especially in the automatic processing of extraterrestrial seismic signals.

A three-axis short-period seismometer is now operating on Mars in the Utopia Planitia region. The noise background correlates well with wind gusts. Although no quakes have been detected in the first 60 days of observation, it is premature to draw any conclusions about the seismicity of Mars. The instrument is expected to return data for at least 2 years.

Repeatable, closely spaced signal sources from large‐capacity air guns and detection and recording of signals using highly flexible, microprocessor‐controlled, digital ocean‐bottom seismographs allow us to acquire high‐quality, large‐offset, marine seismic refraction and reflection data. The acquired data are readily adaptable to various processing techniques originally developed for seismic reflection data. There are several requirements and problems specific to the technique. For example, bubbly signals from one or two large‐capacity air guns are often preferable to bubble‐suppressed signals from tuned arrays in identifying weak arrivals at large offset distances. Recorded water‐wave signals at near ranges provide precise locations of detectors relative to shots.

A three-axis short-period seismometer has been operating on the surface of Mars in the Utopia Planitia region since September 4, 1976. During the first 5 months of operation, approximately 640 hours of high quality data, uncontaminated by lander or wind noise, have been obtained. The detection threshold is estimated to be magnitude 3 to about 200 km and about 6.5 for the planet as a whole. No large events have been seen during this period, a result indicating that Mars is less seismically active than earth. Wind is the major source of noise during the day, although the noise level was at or below the sensitivity threshold of the seismometer for most of the night during the early part of the mission. Winds and therefore the seismic background started to intrude into the nighttime hours starting on sol 119 (a sol is a Martian day). The seismic background correlates well with wind velocity and is proportional to the square of the wind velocity, as is appropriate for turbulent flow. The seismic envelope power spectral density is proportional to frequency to the -0.66 to -0.90 power during windy periods. A possible local seismic event was detected on sol 80. No wind data were obtained at the time, so a wind disturbance cannot be ruled out. However, this event has some unusual characteristics and is similar to local events recorded on earth through a Viking seismometer system. If it is interpreted as a natural seismic event, it has a magnitude of 3 and a distance of 110 km. Preliminary interpretation of later arrivals in the signal suggest a crustal thickness of 15 km at the Utopia Planitia site which is within the range of crustal models derived from the gravity field. More events must be recorded before a firm interpretation can be made of seismicity or crustal structure. One firm conclusion is that the natural background noise on Mars is low and that the wind is the prime noise source. It will be possible to reduce this noise by a factor of 10^3 on future missions by removing the seismometer from the lander, operation of an extremely sensitive seismometer thus being possible on the surface.

Analysis of recent data from lunar seismic events shows significant deviations of P- and S-wave travel times from those expected if the lunar interior were homogeneous below the crust. The interpretation of these data results in a lunar model consisting of at least four and possibly five distinguishable zones whose probable characteristics are discussed.

The horizontal-to-vertical amplitude ratios of the long-period seismograms are reexamined to determine the shear wave velocity distributions at the Apollo 12, 14, 15, and 16 lunar landing sites. Average spectral ratios, computed from a number of impact signals, were compared with spectral ratios calculated for the fundamental mode Rayleigh waves in media consisting of homogeneous, isotropic, horizontal layers. The shear velocities of the best fitting models at the different sites resemble each other and differ from the average for all sites by not more than 20% except for the bottom layer at station 14. The shear velocities increase from 40 m/s at the surface to about 400 m/s at depths between 95 and 160 m at the various sites. Within this depth range the velocity-depth functions are well represented by two piecewise linear segments, although the presence of first-order discontinuities cannot be ruled out.

The structure of the lunar mantle is examined by using data on the decay of shear wave amplitude with distance and the relative arrival times of P and S waves. The new analysis confirms a previous lunar model based primarily upon travel times and more closely defines certain properties of the lunar mantle. A negative shear wave velocity gradient of 0.0013 (km/s)/km, shear wave Q of 4000, and Poisson's ratio of 0.250 plus or minus 0.025 are found for the upper mantle, which lies between the depths of 60 and 300 km. A rapid decrease of shear wave velocity with increasing depth is observed starting at around a 300-km depth, associated with a lower Q for shear waves. Poisson's ratio in the lower part of the middle mantle, which extends to a depth of about 1000 km, is estimated to be 0.36 plus or minus 0.02.

Shallow moonquake data are used to determine the frequency dependence of Q values for both compressional and shear waves in the upper mantle of the moon at frequencies between 3 and 8 Hz. The seismic P wave Q is estimated to be at least 4000 and is nearly independent of frequency or decreases slightly with increasing frequency, while the S wave Q increases from at least 4000 at 3 Hz to at least 7000 at 8 Hz. The rate of increase of Q(S) is approximately proportional to the 0.7 + or - 0.1 power of the frequency above 5 Hz. With the absence of other dissipation mechanisms, compressional heat loss may be a dominant factor in the lunar interior. Uncertainty remains, however, in the absolute values of Q's owing to the largely unknown detailed structure of the lunar upper mantle.

Data relevant to the shallow structure of the moon obtained at the Apollo seismic stations are compared with previously published results of the active seismic experiments. It is concluded that the lunar surface is covered by a layer of low seismic velocity which appears to be equivalent to the lunar regolith defined previously by geological observations. This layer is underlain by a zone of distinctly higher seismic velocity at all of the Apollo landing sites. The regolith thicknesses at the Apollo 11, 12, and 15 sites are estimated from the shear-wave resonance to be 4.4, 3.7, and 4.4 m, respectively. These thicknesses and those determined at the other Apollo sites by the active seismic experiments appear to be correlated with the age determinations and the abundances of extralunar components at the sites.

Unusually long reverberations were recorded from two lunar impacts by a seismic station installed on the lunar surface by the Apollo 12 astronauts. Seismic data from these impacts suggest that the lunar mare in the region of the Apollo 12 landing site consists of material with very low seismic velocities near the surface, with velocity increasing with depth to 5 to 6 kilometers per second (for compressional waves) at a depth of 20 kilometers. Absorption of seismic waves in this structure is extremely low relative to typical continental crustal materials on earth. It is unlikely that a major boundary similar to the crustmantle interface on earth exists in the outer 20 kilometers of the moon. A combination of dispersion and scattering of surface waves probably explains the lunar seismic reverberation. Scattering of these waves implies the presence of heterogeneity within the outer zone of the mare on a scale of from several hundred meters (or less) to several kilometers. Seismic signals from 160 events of natural origin have been recorded during the first 7 months of operation of the Apollo 12 seismic station. At least 26 of the natural events are small moonquakes. Many of the natural events are thought to be meteoroid impacts.

Analysis of seismic signals from man-made impacts, moonquakes, and meteoroid impacts has established the presence of a lunar crust, approximately 60 km thick in the region of the Apollo seismic network; an underlying zone of nearly constant seismic velocity extending to a depth of about 1000 km, referred to as the mantle; and a lunar core, beginning at a depth of about 1000 km, in which shear waves are highly attenuated suggesting the presence of appreciable melting. Seismic velocitites in the crust reach 7 km s−1 beneath the lower-velocity surface zone. This velocity corresponds to that expected for the gabbroic anorthosites found to predominate in the highlands, suggesting that rock of this composition is the major constituent of the lunar crust. The upper mantle velocity of about 8 km s−1 for compressional waves corresponds to those of terrestrial olivines, pyroxenites and peridotites. The deep zone of melting may simply represent the depth at which solidus temperatures are exceeded in the lower mantle. If a silicate interior is assumed, as seems most plausible, minimum temperatures of between 1450°C and 1600°C at a depth of 1000 km are implied. The generation of deep moonquakes, which appear to be concentrated in a zone between 600 km and 1000 km deep, may now be explained as a consequence of the presence of fluids which facilitate dislocation. The preliminary estimate of meteoroid flux, based upon the statistics of seismic signals recorded from lunar impacts, is between one and three orders of magnitude lower than previous estimates from Earth-based measurements.

Wave forms of first arrivals at various distances from explosions in the Gulf of Maine, 1961, were analyzed by Fourier integral analysis. Frequency spectra of the wave forms in the frequency range 2.6 to 25 cps were obtained. The frequency spectra of the refraction arrivals were compared with those of the direct arrivals. Statistical tests show that there is no clear dependence of the frequency content of the arrivals upon distance for either the direct or the refraction arrival, and that the two groups of arrivals definitely belong to two separate groups. Comparison with the results of a model experiment enables an estimate of the minimum possible velocity gradient at the Mohorovičić discontinuity to be made. On the assumption of a linear velocity transition at the boundary, the minimum possible velocity gradient is found to be 4 (km/sec)/km, or the maximum possible thickness of the transition layer to be 12 kilometers.