**1. Introduction**

Subaerial and submarine volcanic landforms originate by primary constructive processes when magma erupts onto the Earth's surface. After the volcanic activity ceases, these volcanic landforms are affected by erosion and weathering, which progressively modify their original morphology. Volcanoes that erupt in environments of relatively high subsidence and low erosion rates can be buried and preserved within sedimentary strata, providing us with an opportunity to investigate the diverse types of volcanic landforms that were formed in the past [1–4].

Volcanic morphologies provide information about the primary and secondary processes that formed them [5–7], and can be used as analogues for understanding buried igneous systems [8, 9]. Our ability to identify buried volcanoes and igneous intrusions emplaced in the shallow (<10 km) layers of the crust has developed immensely over the past four decades in parallel with improvements in the quality and quantity of seismic reflection data. Today, interpretation of seismic reflection datasets indicates that buried volcanoes are characteristic elements of many sedimentary basins globally (e.g. [10–17]).

Seismic interpretation of buried volcanoes benefits from innovations made in the field of sedimentology, in which seismic datasets have been used to analyse in detail the architecture and stratigraphic signature of terrestrial and marine sedimentary systems [18–20]. As noted in [21] *"since the 1960s', attempts to make sense of the diversity of rocks, processes, stratigraphic models and deposition settings of volcanic successions have been aided by major advances in the field of sedimentology"*. Now, seismic reflection data offer unique opportunities to investigate the role of intrusions, host rocks, crustal structures, and relative sea-level variations in the construction and degradation of diverse volcanic landforms [22–24].

Modern seismic reflection datasets allow us to observe the entire architecture of volcanic systems, from the intrusive to the extrusive realms, with resolutions down

### **Figure 1.**

*Seismic reflection visualisation of a small cone-shaped volcano buried in the Taranaki Basin, New Zealand. (a) Shows an amplitude display of a seismic reflection profile across the volcano, coupled with time-slice RMS amplitude display of its plumbing system. (b) 3D opacity-rendered perspective view of the volcano shown in (a) and its shallow (<200 m) plumbing system, in which the low-amplitudes are set as transparent. Note the spatial relationship between the saucer-shaped intrusion and the central vent of the volcano. PrES is the pre-eruptive surface and PoES is the post-eruptive surface.*

**73**

of the seismic signal [35, 36].

*Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins*

to tens of metres [25–27]. In particular, new 3D visualisation methods of igneous seismic geomorphology and analysis of volcanic architectural elements have become valuable tools for interpreting buried volcanoes and their impact on the formation and evolution of the host sedimentary basins. The application of 3D visualisation methods leads for direct comparison of the geomorphic aspects of buried volcanoes with modern and ancient outcropping analogues, allowing us to interpret these buried igneous system in great detail [28, 29]. However, the wide variety of volcanic landforms well-documented in volcanic terrains are still not fully assessed

This chapter highlights the potential for using seismic geomorphology to improve the interpretation of volcanoes buried in sedimentary basins (**Figure 1**). Here, we compare the morphologies of outcropping and buried volcanoes from key localities worldwide. Examples shown in this chapter include description and inter-

) craters and cones, large (>5 km3

The seismic reflection method is a geophysical technique designed to observe the Earth's subsurface indirectly. This method is based on the recording of artificially generated seismic waves that travel into the Earth's geological formations. At the interface of rock bodies with different physical properties, the waves reflect and refract, producing seismic events with wave amplitudes proportional to the contrast in density and velocity of the rocks that bound the interface [30, 31]. Motion- or pressure-sensitive geophones and hydrophones receivers capture the reflected wavefield from the seismic source. A systematic arrangement of the seismic sources and receivers enables the construction of cross-sections that display images of the

Igneous rocks buried in sedimentary basins are often identified by the presence of anomalously high-amplitude reflections within seismic datasets (**Figures 1** and **2**). Characteristically, dense lavas of basaltic composition and mafic intrusions have compressional (P-wave) velocities >5000 ms−1, contrasting with softer sedimentary rocks which commonly have velocities <3000 ms−1 [4, 33, 34]. Despite the straight-forward concept underpinning the identification of igneous rocks based on their high-amplitude reflections, seismic techniques have limitations which leads to uncertainties in the interpretations. Such interpretations are dependent on the quality and resolution of seismic data, which are controlled by geophysical parameters such as wavefield scattering due to changes in rock densities and strata geometries, increasing energy attenuation with depth, and the size of the igneous bodies relative to the wavelength

Distinguishing buried volcanoes from sedimentary strata can be problematic when the igneous rocks have similar physical properties and geometries as the enclosing host rocks. For example, it may be challenging to differentiate volcanoes from carbonate mounds, or sequences of bedded volcaniclastic and siliciclastic rocks [37, 38]. Secondary alteration processes including mineral changes induced

like intrusions. The perceived correlation between the morphology of outcropping and buried volcanoes assist the construction of realistic models from subsurface seismic data, laying the foundations for a new discipline of seismic-reflection volcanology. The information presented in this chapter may have value to geoscientists investigating the impacts of igneous activity on sedimentary basins formation and

evolution, and on the processes that control the large-scale (>102

**2. Principles of seismic interpretation of igneous rocks**

Earth's subsurface, with better quality at depths of <10 km [32].

) composite, shield and

m) architecture of

) lava fields, and subvolcanic sheet-

*DOI: http://dx.doi.org/10.5772/intechopen.95282*

in buried volcanic systems.

pretation of small (<1 km3

caldera volcanoes, voluminous (>10,000 km3

volcanic systems on Earth and related planets.

### *Seismic Geomorphology, Architecture and Stratigraphy of Volcanoes Buried in Sedimentary Basins DOI: http://dx.doi.org/10.5772/intechopen.95282*

to tens of metres [25–27]. In particular, new 3D visualisation methods of igneous seismic geomorphology and analysis of volcanic architectural elements have become valuable tools for interpreting buried volcanoes and their impact on the formation and evolution of the host sedimentary basins. The application of 3D visualisation methods leads for direct comparison of the geomorphic aspects of buried volcanoes with modern and ancient outcropping analogues, allowing us to interpret these buried igneous system in great detail [28, 29]. However, the wide variety of volcanic landforms well-documented in volcanic terrains are still not fully assessed in buried volcanic systems.

This chapter highlights the potential for using seismic geomorphology to improve the interpretation of volcanoes buried in sedimentary basins (**Figure 1**). Here, we compare the morphologies of outcropping and buried volcanoes from key localities worldwide. Examples shown in this chapter include description and interpretation of small (<1 km3 ) craters and cones, large (>5 km3 ) composite, shield and caldera volcanoes, voluminous (>10,000 km3 ) lava fields, and subvolcanic sheetlike intrusions. The perceived correlation between the morphology of outcropping and buried volcanoes assist the construction of realistic models from subsurface seismic data, laying the foundations for a new discipline of seismic-reflection volcanology. The information presented in this chapter may have value to geoscientists investigating the impacts of igneous activity on sedimentary basins formation and evolution, and on the processes that control the large-scale (>102 m) architecture of volcanic systems on Earth and related planets.
