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10 - Modeling approaches in planetary seismology
- from Part III - Modeling approaches
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- By R. C. Weber, NASA Marshall Space Flight Center, M. Knapmeyer, DLR Institute of Planetary Research, M. Panning, University of Florida, N. Schmerr, University of Maryland
- Edited by Vincent C. H. Tong, Birkbeck College, University of London, Rafael A. García, Centre Commissariat à l'Energie Atomique (CEA), Saclay
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- Book:
- Extraterrestrial Seismology
- Published online:
- 05 July 2015
- Print publication:
- 25 June 2015, pp 140-156
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- Chapter
- Export citation
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Summary
Introduction
Of the many geophysical means that can be used to probe a planet's interior, seismology remains the most direct. Given that the seismic data gathered on the Moon over 40 years ago revolutionized our understanding of the Moon and are still being used today to produce new insight into the state of the lunar interior, it is no wonder that many future missions, both real and conceptual, plan to take seismometers to other planets.
To best facilitate the return of high-quality data from these instruments, as well as to further our understanding of the dynamic processes that modify a planet's interior, various modeling approaches are used to quantify parameters such as the amount and distribution of seismicity, tidal deformation, and seismic structure on and of the terrestrial planets. In addition, recent advances in wavefield modeling have permitted a renewed look at seismic energy transmission and the effects of attenuation and scattering, as well as the presence and effect of a core, on recorded seismograms. In this chapter, we will review these approaches.
Site selection for future planetary seismology missions
The ability of a seismic network to accurately locate an event improves as the number of seismometers increases. On Earth we take for granted that any given event will be relatively well located, due to the comparative ease of installation of seismometers. For planetary applications, we cannot count on a large distribution of stations. Various factors including cost, difficulty of installation, instrumentation longevity, and data transmission severely limit the number of instruments that have been or will be deployed on other planetary bodies. In this section, we will review various methods that can be employed to help determine the best landing sites for future planetary seismology missions, in order to maximize their scientific return. We focus here on the Moon and Mars, although many of these methods are adaptable to other planetary bodies.
15 - Seismicity and interior structure of the Moon
- from Part IV - Discoveries of physical structures and processes
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- By M. Knapmeyer, DLR Institute of Planetary Research, R. C. Weber, NASA Marshall Space Flight Center
- Edited by Vincent C. H. Tong, Birkbeck College, University of London, Rafael A. García, Centre Commissariat à l'Energie Atomique (CEA), Saclay
-
- Book:
- Extraterrestrial Seismology
- Published online:
- 05 July 2015
- Print publication:
- 25 June 2015, pp 203-224
-
- Chapter
- Export citation
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Summary
The beginning of the seismological inv estigation of the Moon dates back to the beginning of space flight: A working group implemented by NASA in 1959 (Hall, 1977) suggested the development of a seismometer for a hard landing on the Moon. This resulted in Ranger missions 3 to 5, which all unfortunately failed for technical reasons (Hall, 1977). The first measurement of elastic properties of lunar soil was conducted by the Surveyor landers a few years later (Christensen et al., 1968).
Besides these early attempts, seismological studies of the Moon divide into two phases: The first one saw the installation of a seismometer network on the Moon, starting with Apollo 11 on July 20, 1969 (Apollo 11 Mission Report, 1969), followed by the collection of continuous data until network shutdown on September 30, 1977 (Bates et al., 1979), and, in parallel and ongoing until the early 1990s, the analysis of the data. The second phase began in the late 1990s, when cheap computer power allowed for massive data processing on desktop workstations and the application of new methods.
This chapter aims to give a sketch of the Moon as it results from these two phases. The following sections will first describe the different types of seismic events observed on the Moon, and then detail the structure of the main layers of the lunar interior, i.e., the crust, mantle, and core. A summary section finally gives an overview of the present-day concept of the interior structure of the Moon.
Seismic sources and seismicity
Both endogenous and exogenous sources create seismic waves on the Moon. It is thus common to speak of “events” rather than “quakes,” unless the type of source has been identified. However, analysis of the spatial and chronological distribution of events, and of seismogram characteristics, leads to the identification of several classes of sources.