Laura Nichele Raines and Heather Lehto, Ph.D. Angelo State University, Department of Physics and Geosciences Introduction Acknowledgements Results References Discussion Methods 1 Conclusion Dr. Heather Lehto, Michael Raines, Josue Rodriguez, Pierfrancesco Burrato, Angelo State University, Angelo State University Undergraduate Research Grant, Angelo State University Dept. of Physics and Geosciences. Figure 1: This map represents the study area, which is Italy. A map is included so that you can specifically see what areas I have studied. Badal, José, et al. "S-Wave Velocity Images Of The Dead Sea Basin Provided By Ambient Seismic Noise." Journal Of Asian Earth Sciences 75.(2013): ScienceDirect. Web. 27 Apr Civetta, L., et al. "Thermal And Geochemical Constraints On The ‘Deep’ Magmatic Structure Of Mt. Vesuvius." Journal Of Volcanology And Geothermal Research 133.The Neapolitan Volcanoes: Vesuvius, Campi Flegrei and Ischia (2004): ScienceDirect. Web. 27 Apr Correale, Alessandra, et al. 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"H2O-Fluid-Saturated Melting Of Subducted Continental Crust Facilitates Exhumation Of Ultrahigh-Pressure Rocks In Continental Subduction Zones." Earth & Planetary Science Letters 428.(2015): Science & Technology Collection. Web. 27 Apr Špičák, Aleš, Václav Hanuš, and Jiří Vaněk. "Seismotectonic Pattern And The Source Region Of Volcanism In The Central Part Of Sunda Arc." Journal Of Asian Earth Sciences 25.(2005): ScienceDirect. Web. 27 Apr Špičák, Aleš, Václav Hanuš, and Jiřı́ Vaněk. "Seismicity Pattern: An Indicator Of Source Region Of Volcanism At Convergent Plate Margins." Physics Of The Earth And Planetary Interiors 141.Structure and tectonics of convergent plate margins (2004): ScienceDirect. Web. 27 Apr There is a section of Italy that has sparked a great deal of interest when looking at the shear wave velocities. Italy’s upper island, Sardinia, and a portion of Italy above the heal host this puzzling data. One location has a section of earthquakes along the Wadati-Benioff Zone that disappear. The earthquakes, which are within a subduction zone, are absent when there is a higher shear wave (s- wave) zone present. In this Wadati-Benioff Zone where the earthquakes do not occur, it is almost as if the higher velocities inhibit the earthquakes, because after the high velocity zone has ended, the earthquakes resume. It could be possible that the earthquakes aren’t occurring in these areas because of special conditions along the Wadati-Benioff Zone. There is also a location, in Sicily, where there is a very low velocity zone that has all the earthquakes above or surrounding it. In Sicily, these earthquakes that happen above the low velocity zone could be related to the volcanic activity on the island. Used a program from Incorporated Research Institute for Seismology (IRIS) called IRIS Earth Model Collaboration (EMC) to generate the cross sections, slice stacks, and horizontal views of Italy using the tomographic velocity model Kustowski, Ekstrom, Dziewonski (2008), and also used it for the earthquake locations from the IRIS global catalog. Tomographic Models that have the most useful information are cross sections, stacks, and horizontal slice viewer. Used data from existing studies to help explain the problems. Cross Sections A’ A BB’ Map of Italy The earthquakes follow the curve of Italy. Earthquakes surround the low velocity zone possibly due to magma formation in that area. Earthquakes are in the slab but not in the low velocity zone. Cross Section A-A’ From the data collected, there is a section of earthquakes that disappear along the subduction zone beneath the lower portion of Sardinia and a small section of Italy (Figure 4). These earthquakes along the Wadati-Benioff Zone that disappear could be caused from a change in pore fluid pressure along the plate (Davis and Reynolds, 1996). Davis and Reynolds (1996) stated that elevated pore pressure can decrease ultimate and rupture strength along with a decrease in ductility. Disappearing earthquakes could possibly be caused from fluid pressure which counteracts the stress that comes from volatiles, typically water, which is driven off the subducting plate (Davis and Reynolds, 1996). There is a higher velocity area, represented by the blue on the cross sections, that appears to stop the earthquakes. After the higher velocity zone has ended, the earthquakes of all sizes resume to normal levels. The reason this section is so interesting is because there is an undefined gap of missing earthquakes along the subduction zone. Cross Section B-B’ There is also a subduction zone that occurs in Sicily, although it is not as prominent as the one in Sardinia and portions of Italy (Figure 5). Most of the earthquakes occurring along this section of Sicily in the shallow crust, but not the slab, could be related to fault zones that run through the area or volcanic activity. The s-wave velocity in Sicily is significantly lower than that of Sardinia and portions of Italy. Figure 4: A-A’ cross section is from the lower portion of Sardinia and a small section of Italy. A subduction zone appears to be within this cross section. In addition to the subduction zone, there is an absence of earthquakes that coincides with the high velocity zone. Figure 5: B-B’ cross section is across the upper part of Sicily. Rather shallow earthquakes seem to be linked to crustal faults and volcanoes. A subduction zone is also located here. Slice Stacks Figure 3: These slice stacks represent the overall s- wave velocity of Italy from depths of 25km to 200km. Note the area of low velocity is centered between Sardinia and mid Italy. Below 200 km the low velocity zone disappears. Figure 2: Map of the seismic behavior seismic across Italy. A-A’ and B-B’ represent the locations of cross sections in figures 4 and 5. Note that the earthquakes surround the low velocity zone. There are two portions of Italy that raise curiosity. The main section has missing earthquakes along the Wadati-Benioff Zone. Disappearing earthquakes could be caused from a change in pressure or lubrication of the subducting tectonic plate. The other location with the relatively low s-wave velocity could have the earthquakes caused from either volcanic activity or because of where it sits on the faults of Italy.