A discussion about how the deep moonquakes are triggered by tidal stress

doi:10.7523/j.issn.2095-6134.2016.01.013

Abstract

Abstract:

Most moonquakes recorded are deep moonquakes that occur at depths of 700-1 200 km, and have a period of about 27 days. We use parallel finite element method and a model with million grids to simulate the tidal stress field and displacement field of the moon numerically. The results show that the maximum shear stress varies with depth. If the moon has a liquid core with a radius of about 700 km or if the moon has a smaller core but the materials at the bottom of lunar mantle are partially molten, the depth of the maximum shear stress will coincide with the depth of the deep moonquakes. The proposition that the moon has a core is lack of sound seismological evidence.Our calculation provides another approach and our result inclines to the suggestion that the moon has a liquid core.

Key words: tidal stress, moonquake, parallel computation, finite element method

CLC Number:

P184

ZHANG Bei, ZHANG Huai, SHI Yaolin. A discussion about how the deep moonquakes are triggered by tidal stress[J]. , 2016, 33(1): 82-88.

References

[1] Lognonné P,Mosser B. Planetary seismology[J]. Surveys in Geophysics, 1993, 14(3): 239-302.
[2] Wieczorek M A, Jolliff B L, Khan A, et al. The Constitution and Structure of the Lunar Interior[J]. Reviews in Mineralogy and Geochemistry, 2006, 60(1): 221-364.
[3] Bulow R C, Johnson C L, Bills B G, et al. Temporal and spatial properties of some deep moonquake clusters[J]. Journal of Geophysical Research, 2007, 112(E9).
[4] Koyama J. Chaotic occurrence of some deep moonquakes // 36th Annual Lunar and Planetary Science Conference, 2005,36: 1 077.
[5] Bills B G, Bulow R, Johnson C L. Influence of earth-moon orbit geometry on deep moonquake occurrence times[C]//Lunar and Planetary Institute Science Conference Abstracts. 2008: 1 735.
[6] Frohlich C, Nakamura Y. Geographic variations in the tidal control of deep moonquake nests and speculation about their mechanical origin[C]//Lunar and Planetary Institute Science Conference Abstracts. 2007, 38: 1 749.
[7] 丰海. 利用重力场和地形数据反演月壳厚度[J]. 大地测量与地球动力学, 2009, 29(3): 131-134.
[8] 朱桂芝, 张怀, 石耀霖. 优化地球三维有限元计算网格的一种方法[J]. 中国科学院研究生院学报, 2006, 23(5): 676-680.
[9] 陈绍林, 张怀, 朱桂芝,等. 自转速率快速变化引起的全球位移场和应力场[J]. 地震, 2008, 28(4): 1-12.
[10] Khan A. A new seismic velocity model for the moon from a Monte Carlo inversion of the Apollo lunar seismic data[J]. Geophysical Research Letters, 2000, 27(11): 1 591-1 594.
[11] Lognonn P, Gagnepain-Beyneix J,Chenet H. A new seismic model of the moon: implications for structure, thermal evolution and formation of the Moon[J]. Earth and Planetary Science letters. 2003, 211(1/2): 27-44.
[12] Gagnepain-Beyneix J, Lognonn P, Chenet H, et al. A seismic model of the lunar mantle and constraints on temperature and mineralogy[J]. Physics of The Earth and Planetary Interiors, 2006, 159(3/4): 140-166.
[13] 柯宝贵. 应用Lane-Emden方程分析下月幔厚度与月核半径大小[J]. 地球物理学报, 2009, 52(5): 1 208-1 213.
[14] 占伟,李斐. 月球内部构造研究综述[J]. 地球物理学进展, 2007, 22(3): 737-742.
[15] 张承志. 月球和火星内部结构模型的比较[J]. 南京大学学报:自然科学版, 1990, 24(4): 575-587.
[16] 欧阳自远. 月球科学概论[M]. 北京: 中国宇航出版社, 2005.
[17] Latham G, Ewing M, Dorman J, et al. Moonquakes and lunar tectonism[J]. Earth, Moon, and Planets, 1972, 4(3): 373-382.
[18] Goins N R, Dainty A M, Toksoz M N. Seismic energy release of the moon[J]. Journal of Geophysical Research, 1981, 86: 378-388.
[19] Wells D L, Coppersmith K J. New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement[J]. Bulletin of the Seismological Society of America, 1994, 84(4): 974-1 002.
[20] Hanks T C, Anderson D L. Origin, evolution and present thermal state of the Moon[J]. Physics of The Earth and Planetary Interiors, 1972 (5): 409-425.
[21] Tozer D C. The moon's thermal state and an interpretation of the lunar electrical conductivity distribution[J]. Earth, Moon, and Planets. 1972, 5(1): 90-105.
[22] Toksöz M N, Solomon S C. Thermal history and evolution of the Moon[J]. Earth, Moon, and Planets, 1973, 7(3): 251-278.
[23] Khan A. Constraining the composition and thermal state of the moon from an inversion of electromagnetic lunar day-side transfer functions[J]. Earth and Planetary Science Letters, 2006, 248(3/4): 579-598.
[24] Khan A, Maclennan J, Taylor S R, et al. Are the earth and the moon compositionally alike? Inferences on lunar composition and implications for lunar origin and evolution from geophysical modeling[J]. Journal of Geophysical Research, 2006, 111(E05005). doi:10.1029/2005JE002608.
[25] Khan A. Joint inversion of seismic and gravity data for lunar composition and thermal state[J]. Geophysical Journal International, 2007, 168(10): 243-258.
[26] Nakamura Y. A1 moonquakes:Source distribution and mechanism[C]//Lunar and Planetary Science Conference Proceedings.1978, 9: 3 589-3 607.
[27] Nakamura Y. New identification of deep moonquakes in the Apollo lunar seismic data[J]. Physics of The Earth and Planetary Interiors, 2003, 139: 197-205.
[28] Nakamura Y. Within-nest hypocenter distribution and waveform polarization of deep moonquakes and their possible implications [C]//Lunar and Planetary Institute Science Conference Abstracts. 2007,38:1 160.