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Determining Moho Depth beneath Sedimentary Basins Using Regional Pn Multiples

Yu, Chunquan and Zhan, Zhongwen and Hauksson, Egill and Cochran, Elizabeth S. and Helmberger, Donald V. (2019) Determining Moho Depth beneath Sedimentary Basins Using Regional Pn Multiples. Bulletin of the Seismological Society of America, 109 (3). pp. 1171-1179. ISSN 0037-1106. doi:10.1785/0120180325.

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The study of the Moho beneath thick sedimentary basins involving natural earthquakes is challenging, as low‐velocity materials often cause strong reverberations that mask Moho signals. Here, we develop a method to determine the depth of the Moho by taking advantage of the presence of the sediments. The method utilizes the first Pn crustal multiple from regional earthquakes PnPn and its differential travel time with respect to Pn. PnPn is usually weak in amplitude; thus, it is difficult to identify in regions without a sedimentary cover. However, PnPn is significantly amplified in the presence of low‐velocity sediments because of an increase in the near‐surface P‐to‐P reflection coefficient. The arrival time, amplitude, and wave shape of PnPn, if normalized by the reference Pn, are insensitive to earthquake source parameters, such as focal mechanism and focal depth. We demonstrate the potential of this method using both 1D and 2D waveform simulations. Synthetic waveforms suggest that PmpPn and PnPmp (one Pn leg merges to PmP near the source or the receiver) largely contribute to the PnPn amplitudes, which depend on the near‐surface structure at their free‐surface P‐to‐P reflection points. We further validate the method with two field examples in the Imperial Valley; one is near the United States–Mexico border, and the other is in Oklahoma in the central United States. Both examples suggest that the method can be used to study the Moho either near the source or the receiver.

Item Type:Article
Related URLs:
URLURL TypeDescription
Yu, Chunquan0000-0001-8681-8572
Zhan, Zhongwen0000-0002-5586-2607
Hauksson, Egill0000-0002-6834-5051
Cochran, Elizabeth S.0000-0003-2485-4484
Additional Information:© 2019 Seismological Society of America. Manuscript received 6 December 2018; Published Online 7 May 2019. Data and Resources: Broadband waveforms of southern California seismic stations were retrieved from the Southern California Seismic Network (SCSN), and USArray stations were retrieved from the Incorporated Research Institutions for Seismology (IRIS) Data Management Center (, last accessed March 2019). The focal mechanism of the 2011 Mw 5.7 Oklahoma earthquake is from the U.S. Geological Survey National Earthquake Information Center (, last accessed March 2019). Depth of the 2010 El Mayor–Cucapah earthquake sequence is determined in the unpublished manuscript: C. Yu, E. Hauksson, Z. Zhan, E. S. Cochran, and D. V. Helmberger, “Depth Determination of the 2010 El Mayor–Cucapah Earthquake Sequence (M4.0),” J. Geophys. Res. (in revision). The authors thank Chuck Langston and an anonymous reviewer for constructive reviews. Comments from Tom Brocher and Fred Pollitz are appreciated. This research was supported by National Science Foundation (NSF) Grant Numbers 1722879 and 1829496; U.S. Geological Survey/National Earthquake Hazards Reduction Program (USGS/NEHRP) Grant Numbers G16AP00147 and G18AP00028; and by the Southern California Earthquake Center (SCEC) (Award Number 17044), which is funded by NSF Cooperative Agreement EAR‐1033462 and USGS Cooperative Agreement G12AC20038. The authors used waveforms and parametric data from the Caltech/USGS Southern California Seismic Network (SCSN), doi:; stored at the Southern California Earthquake Data Center, doi:
Group:Seismological Laboratory
Funding AgencyGrant Number
Southern California Earthquake Center (SCEC)17044
Issue or Number:3
Record Number:CaltechAUTHORS:20190508-082435371
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Official Citation:Chunquan Yu, Zhongwen Zhan, Egill Hauksson, Elizabeth S. Cochran, Donald V. Helmberger; Determining Moho Depth beneath Sedimentary Basins Using Regional Pn Multiples. Bulletin of the Seismological Society of America ; 109 (3): 1171–1179. doi:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95336
Deposited By: Tony Diaz
Deposited On:08 May 2019 15:43
Last Modified:16 Nov 2021 17:11

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