The Seismically Active Lobate Scarps and Coseismic Lunar Boulder Avalanches Triggered by 3 January 1975 (MW 4.1) Shallow Moonquake. Issue 14 (22nd July 2019)

• Record Type: Journal Article
• Authors: Kumar, P. Senthil; Mohanty, Rupali; Lakshmi, K. Jaya Prasanna; Raghukanth, S. T. G.; Dabhu, Anjali C.; Rajasekhar, R. P.; Menon, Rajeev
• Is Part Of: Geophysical research letters. Volume 46:Issue 14(2019)
• Page Start: 7972
• Page End: 7981
• Publication Date: 2019-07-22
• Subjects: shallow moonquake -- lobate scarps -- boulder falls -- recent seismicity -- seismic ground motion -- seismo‐tectonics; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2019GL083580
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: On 3 January 1975, the largest shallow moonquake ( M W 4.1) occurred at Laue impact crater on the Moon. The fault responsible for the moonquake and origins of coseismic boulder avalanches are unknown. Our study reveals a set of previously unreported, seismically active, young lobate scarps near the epicenter. In addition, hundreds of boulder falls are observed on the interior walls of two impact craters on either side of the lobate scarps. The varying preservation levels and crater size‐frequency distributions of impact craters superimposed on the boulder falls indicate their episodic origins at 1.6 Ma and during the 1975 shallow moonquake. Our ground motion simulations confirm that the M W 4.1 moonquake along the lobate scarp at 1‐ to 5‐km focal depths produced strong ground shaking that triggered the boulder avalanches. Also, the fault slip along the Lorentz basin wall beneath the Laue crater floor produced the lobate scarps and the shallow moonquakes. Plain Language Summary: Like Earth, the Moon is also seismically active but with relatively lesser intensity. The seismometers installed by the Apollo missions detected 28 shallow moonquakes during 1969–1977. The moonquake that occurred at Laue crater on 3 January 1975 is the largest recorded moonquake ( M W 4.1). Our analysis of high‐resolution satellite images and topographic data obtained by NASA's Lunar Reconnaissance Orbiter mission aided in the discovery of a set of young lobate scarps near the epicenter and its genetic link to the 1975 moonquake. The moonquake also generated strong ground motion around the epicenter and triggered formation of coseismic boulder avalanches on the interior walls of nearby impact craters. We also found that boulder avalanches were formed during an earlier episode of seismic activity at 1.6 Ma. Furthermore, we deduce that the lobate scarps at Laue crater were formed in response to the reactivation of the basin wall normal fault of Lorentz peak‐ring basin. Our study indicates that the lobate scarps in Laue crater are seismically active and their seismic activity could be further studied during future landing missions. Key Points: A set of lobate scarps responsible for the 3 January 1975 shallow moonquake ( M W 4.1) has been detected in Laue crater floor Coseismic boulder avalanches of different ages have been identified on the interior walls of impact craters near the epicenter Fault slip along the Lorentz basin wall beneath the Laue crater floor produced the lobate scarps and shallow moonquakes