A three‐dimensional QP imaging of the shallowest subsurface of Campi Flegrei offshore caldera, southern Italy. Issue 21 (12th November 2016)

• Record Type: Journal Article
• Authors: Serlenga, Vincenzo; de Lorenzo, Salvatore; Russo, Guido; Amoroso, Ortensia; Garambois, Stephane; Virieux, Jean; Zollo, Aldo
• Is Part Of: Geophysical research letters. Volume 43:Issue 21(2016)
• Page Start: 11, 209
• Page End: 11, 218
• Publication Date: 2016-11-12
• Subjects: attenuation tomography -- saturated shallow sediments; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2016GL071140
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: To improve the knowledge of the shallowest subsurface of Campi Flegrei caldera, a 3‐D P wave attenuation tomography of the area was performed. We analyzed about 18, 000 active seismic traces, which provided a data set of 11, 873 Δ t * measurements, e.g., the differential travel times to quality factor ratios. These were inverted through an adapted tomographic inversion procedure. The 3‐D tomographic images reveal an average QP about 70, interpreted as water‐saturated volcanic and marine sediments. An arc‐like, low‐ QP structure at 0.5–1 km depths was interpreted as a densely fractured, fluid‐saturated rock volume, well matching the buried rim of Campi Flegrei caldera. The spatial distribution of high‐ and low‐ QP bodies in the inner caldera is correlated with low‐ Vp values and may reflect either the differences in the percentage of fluid saturation of sediments or the presence of vapor state fluids beneath fumarole manifestations. Plain Language Summary: Volcanic risk is one of the most dangerous natural risks in the world. Due to massive population in its surroundings, Campi Flegrei Volcano, which is still an active volcano in Southern Italy, is one of the most dangerous volcanoes in the world. We investigate how seismic waves are attenuated in the first kilometer of depth of the subsoil of the marine part of this volcano. In that way, presence of fractures in the rocks, of fluids in the sediments, of gas may be inferred. We conclude that Campi Flegrei caldera is characterized by a fluid‐filled and densely‐fractured buried rim. The fluids in depth located in this part of volcano may be responsible for the manifestations of gas emissions which may be seen at the surface. Moreover, other zones of possible fluid accumulation have been detected, both in liquid phase and in gaseous phase. Key Points: Tuffites and marine sediments are characterized by QP values less than 40 High‐ QP anomalies may be explained as consolidated volcanic materials or fluid effects A fluid‐filled densely fractured rock volume has been imaged as the rim of caldera