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Determining Moho Depth Across Montana Using Receiver Functions

Permanent Link: http://ufdc.ufl.edu/UFE0041757/00001

Material Information

Title: Determining Moho Depth Across Montana Using Receiver Functions Implications for the Existence of a High Velocity Lower Crustal Layer Beneath the State of Montana
Physical Description: 1 online resource (81 p.)
Language: english
Creator: Sirianni, Robert
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: function, lcl, montana, receiver
Geological Sciences -- Dissertations, Academic -- UF
Genre: Geology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Masters of Science DETERMING MOHO DEPTH ACROSS MONTANA USING RECEIVER FUNCTIONS: IMPLICATIONS FOR THE EXISTENCE OF A HIGH VELOCITY LOWER CRUSTAL LAYER BENEATH THE STATE OF MONTANA By Robert Thomas Sirianni May 2010 Chair: Raymond M. Russo Major: Geology The active source Deep Probe-SAREX projects (Henstock et al., 1998; Clowes et al., 2002; Gorman et al., 2002) imaged a high velocity lower crustal layer (LCL), ~20-35 km thick, within the Wyoming Craton (WC) and Medicine Hat Block (MHB), positioned beneath the states of Wyoming and Montana, and north into Canada, during the Deep Probe-SAREX seismic refraction projects. The layer is relatively thick (~25 km) and propagates P waves at velocities between 7-8 km/sec, giving the so-called 7x layer its name. The LCL is not well defined on the north-south Deep Probe-SAREX line in the USA due to poor resolution (shot spacing ~700 km), and the linearity of the seismic sampling does not define the layer's extent to the east or west. We used receiver functions (RFs) at 6 permanent ANSS stations derived from 35 events to determine Moho depth beneath each station. Moho depth determination will help aid in determining whether or not the 7x layer is present at each location. If the crust is thicker than average crustal values or previously reported thicknesses for these stations, it is possible that the layer does exist, on a per station basis. The seismic stations are located across Montana and are the reference points for this study. The RFs resolve 13 any extant sharp velocity contrast boundaries, such as horizontal and dipping beds and juxtaposed tectonic units. Scattering of P-to-S conversions off these sharp velocity interfaces helped identify the lateral extent of the high velocity lower crustal layer (LCL). Using an algorithm developed by Zhu and Kanamori (2000) it is possible to use the Ps, PpPs, and PpSs+PsPs phases to predict crustal thicknesses and Vp/Vs ratios for these stations. The results indicate that BOZ and MSO, located in the Northern Rocky Mountains, have, in general, thicker crust and higher Vp/Vs ratios. High Vp/Vs ratios are diagnostic of propagation through mafic crustal rocks and are consistent with the presence of the LCL beneath these two stations. Continental crust at stations DGMT and LAO is thinner and Vp/Vs ratios are lower than at BOZ and MSO. These two stations are situated in the Williston Basin, and sedimentary basins generally are characterized by higher Vp/Vs ratios, but the RF signals at these stations are dominated by the predominately silica-rich basement beneath the Williston Basin strata. The high Vp/Vs ratios of the stations in the Rocky Mountains provide some supporting evidence for a hypothesized mafic underplating event, occurring after the amalgamation of Laurentia was complete. The crustal thickness results of this study compare well with previous studies throughout the Northern Rocky Mountains. Values, in general, are within a few kilometers of observed receiver function depths. The largest discrepancies arise when structural complexity becomes too significant to ignore in radial receiver function analysis.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Robert Sirianni.
Thesis: Thesis (M.S.)--University of Florida, 2010.
Local: Adviser: Russo, Raymond M.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0041757:00001

Permanent Link: http://ufdc.ufl.edu/UFE0041757/00001

Material Information

Title: Determining Moho Depth Across Montana Using Receiver Functions Implications for the Existence of a High Velocity Lower Crustal Layer Beneath the State of Montana
Physical Description: 1 online resource (81 p.)
Language: english
Creator: Sirianni, Robert
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: function, lcl, montana, receiver
Geological Sciences -- Dissertations, Academic -- UF
Genre: Geology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Masters of Science DETERMING MOHO DEPTH ACROSS MONTANA USING RECEIVER FUNCTIONS: IMPLICATIONS FOR THE EXISTENCE OF A HIGH VELOCITY LOWER CRUSTAL LAYER BENEATH THE STATE OF MONTANA By Robert Thomas Sirianni May 2010 Chair: Raymond M. Russo Major: Geology The active source Deep Probe-SAREX projects (Henstock et al., 1998; Clowes et al., 2002; Gorman et al., 2002) imaged a high velocity lower crustal layer (LCL), ~20-35 km thick, within the Wyoming Craton (WC) and Medicine Hat Block (MHB), positioned beneath the states of Wyoming and Montana, and north into Canada, during the Deep Probe-SAREX seismic refraction projects. The layer is relatively thick (~25 km) and propagates P waves at velocities between 7-8 km/sec, giving the so-called 7x layer its name. The LCL is not well defined on the north-south Deep Probe-SAREX line in the USA due to poor resolution (shot spacing ~700 km), and the linearity of the seismic sampling does not define the layer's extent to the east or west. We used receiver functions (RFs) at 6 permanent ANSS stations derived from 35 events to determine Moho depth beneath each station. Moho depth determination will help aid in determining whether or not the 7x layer is present at each location. If the crust is thicker than average crustal values or previously reported thicknesses for these stations, it is possible that the layer does exist, on a per station basis. The seismic stations are located across Montana and are the reference points for this study. The RFs resolve 13 any extant sharp velocity contrast boundaries, such as horizontal and dipping beds and juxtaposed tectonic units. Scattering of P-to-S conversions off these sharp velocity interfaces helped identify the lateral extent of the high velocity lower crustal layer (LCL). Using an algorithm developed by Zhu and Kanamori (2000) it is possible to use the Ps, PpPs, and PpSs+PsPs phases to predict crustal thicknesses and Vp/Vs ratios for these stations. The results indicate that BOZ and MSO, located in the Northern Rocky Mountains, have, in general, thicker crust and higher Vp/Vs ratios. High Vp/Vs ratios are diagnostic of propagation through mafic crustal rocks and are consistent with the presence of the LCL beneath these two stations. Continental crust at stations DGMT and LAO is thinner and Vp/Vs ratios are lower than at BOZ and MSO. These two stations are situated in the Williston Basin, and sedimentary basins generally are characterized by higher Vp/Vs ratios, but the RF signals at these stations are dominated by the predominately silica-rich basement beneath the Williston Basin strata. The high Vp/Vs ratios of the stations in the Rocky Mountains provide some supporting evidence for a hypothesized mafic underplating event, occurring after the amalgamation of Laurentia was complete. The crustal thickness results of this study compare well with previous studies throughout the Northern Rocky Mountains. Values, in general, are within a few kilometers of observed receiver function depths. The largest discrepancies arise when structural complexity becomes too significant to ignore in radial receiver function analysis.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Robert Sirianni.
Thesis: Thesis (M.S.)--University of Florida, 2010.
Local: Adviser: Russo, Raymond M.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0041757:00001


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