# Imaging Top of Volcanic Mounds Using Seismic Time- and Depth-Domain Data Processing
## 1 Introduction  
Areas affected by volcanic eruptions such as basalt lava flows or fissure vents are frequently found across the Earth's surface, arousing considerable scientific interest [1]. The volcanic subsurface can be explored through the use of geophysical methodologies, e.g., gravity, magnetic and seismic surveys [2; 3; 4]. In the seismic exploration data, the volcanic area shows strong amplitude events due to the relatively high contrast of density and reflectivity [5]. Abrupt collapses, unexpected faults and subsidence are other common characteristics of magmatic intrusions resulting from volcanic activity [6]. Aspects of the reflection signal's diversity present challenges in seismic data processing, particularly in the estimation of velocity information [6; 7; 8]. Since the seismic data related to volcanic activity have less commercial usefulness than the exploration data for hydrocarbon development, the complicated data-processing procedure is often not applied. In addition, representative research cases in which the velocity was obtained by processing seismic data have used geophone-recorded data, which contain accurate depth information [7; 8].  
The increase in the scientific and/or engineering curiosity regarding volcanic regions means that additional velocity-specific seismic data processing is required. Carbon capture and storage (CCS) projects have led to expanded efforts to assess the storage, from depleted reservoirs to saline aquifers with upper volcanic cap rocks [9; 10]. Saline aquifers have the advantage of large storage volume but require a sealing structure in order to safely store CO\({}_{2}\)[10; 11]. Basalt flow, due to its rock-physical properties, may be a suitable cap rock for the storing CO\({}_{2}\) in the aquifer beneath the flow. Moreover, the mineralizationof carbon can prevent the migration of CO2, which leads to favorable stabilization for long-term storage [12]. To use basalt flow as the cap rock for CO2 storage, accurate verification of the fracture zone and deformation should be carried out in both the time and depth domains [13]. Optimized seismic data processing for basalt flow can provide an accurate understanding of the possible fracture zone due to velocity anomalies and possible deformations by subtle depth conversion.  
In the Southern Continental Shelf of Korea (SCSK), there is an independent structure formed by volcanic events, showing the potential of CCS [14; 15]. Two-dimensional seismic surveys were executed in 2018 across the areas of the SCSK to calculate the storage capacity of CO2 for the saline aquifer. Determination of the exact depth of the target is important when drilling injections and monitoring wells [16]. In the seismic sections, by applying only time-domain processing, basalt flow shows high reflectivity contrast, which might lead to errors during the geological interpretation. The boundary and lateral expansion of basalt flow are not easy to analyze in terms of potential cap rocks for CO2 storage.  
To enhance the seismic sections' resolution, we applied both time-domain and depth-domain processing using the MVA technique [17; 18]. MVA is able to determine the velocity with high accuracy by considering subtle changes in spatial velocities. We demonstrated the iterated velocity and determined the accurate velocity from the flatness of the collected CRP gathers. In order to confirm the effectiveness of our processing, amplitude contour and root mean square (RMS) maps derived before and after MVA application were compared. If the precise boundary and depth of volcanic mounds can be defined, CO2 storage capacity can be calculated with confidence.