[Paper Review] Crustal Structure Imaging of Ghana from Single-Station Ambient Noise Autocorrelations and Earthquake Arrival Time Inversion

Hamzeh Mohammadigheymasi, Courage K. Letsa+6 more|arXiv (Cornell University)|Mar 11, 2026

Seismic Waves and Analysis0 citations

TL;DR

The paper images southern Ghana's crust using single-station ambient noise autocorrelations and augments it with a local earthquake velocity model to convert travel times to depth, yielding new basement depth constraints and an updated seismicity catalog.

ABSTRACT

The crustal architecture of southern Ghana remains inadequately resolved despite its tectonic significance and resource potential. Existing geological and geophysical studies provide only broad constraints on crustal composition, lacking the resolution to accurately define sediment-basement interfaces or intra-crustal stratigraphy. To address these limitations, we employ single-station ambient noise autocorrelation (SSANA) on continuous waveform data from the Ghana Digital Seismic Network (GHDSN). We extract P-wave reflectivity responses using a processing sequence that involves data pre-processing, Phase Cross-Correlation (PCC) for robust noise correlation, and phase-weighted stacking (PWS) of the derived autocorrelograms. This procedure yields a two-way travel-time (TWT) function representing the zero-offset P-wave reflection response beneath each station, enabling high-resolution imaging of the stratified crustal column. To facilitate depth conversion, we develop an enhanced one-dimensional crustal velocity model for the region. Using a compiled dataset of local earthquake P- and S-wave arrival times from the GHDSN and an additional station in Cote d'Ivoire, we perform a joint inversion via a grid-search algorithm to derive a regional 1D velocity structure. Our results provide new constraints on the depth and configuration of the Paleozoic basement beneath the Voltaian Basin, demonstrating the efficacy of ambient noise autocorrelation for crustal imaging in sparsely instrumented regions. We also present an updated seismicity catalog, relocated using the new velocity model, and analyze the spatial clustering of seismicity in southern Ghana. This study highlights the utility of passive seismic methods for elucidating crustal structure and evaluating resources in intraplate West Africa and analogous Precambrian terrains.

Motivation & Objective

• Address the poorly constrained crustal structure of southern Ghana.
• Image the crustal column by extracting P-wave reflectivity from ambient noise at single stations.
• Develop a regionally representative 1-D crustal velocity model for accurate depth conversion.
• Relocate earthquakes with the new velocity model and discuss tectonic implications.

Proposed method

• Process six GHDSN broadband station records (and one Côte d’Ivoire station) with single-station ambient noise autocorrelation to obtain P-wave reflectivity as a function of two-way travel time.
• Use Phase Cross-Correlation (PCC) to extract robust phase-coherent reflections from hourly autocorrelograms.
• Apply Phase Weighted Stacking (PWS) to daily PCCs to enhance coherent arrivals and obtain daily TWT reflection series.
• Develop a 1-D regional velocity model via local earthquake arrival-time inversion, incorporating local HDD data and an additional western station to improve azimuthal coverage.
• Convert TWT reflectivity sections to depth using the new velocity model to image sediment–basement interfaces.
• Relocate and update the southern Ghana seismicity catalog using the new velocity model.

Experimental results

Research questions

• RQ1 Can SSANA (single-station ambient noise autocorrelation) reliably image crustal reflectivity beneath sparse networks in southern Ghana?
• RQ2 What does a locally constrained 1-D velocity model imply for depth conversion of P-wave reflections in this region?
• RQ3 Where are the major crustal interfaces (sediment–basement) beneath southern Ghana and how do they relate to known geological units?
• RQ4 How does the updated velocity model affect earthquake relocation and regional seismicity patterns?

Key findings

• SSANA with PCC and PWS yields interpretable P-wave reflection responses beneath each station in two frequency bands (3–13 Hz for shallow features; 1–6 Hz for deeper structures).
• A new regionally representative 1-D crustal velocity model was derived via local earthquake tomography, improving depth conversion of the SSANA results.
• The study provides new constraints on the depth and configuration of the Paleozoic basement beneath the Voltaian Basin.
• An updated seismicity catalog for southern Ghana is presented, with relocations informed by the new velocity model.
• The results demonstrate the utility of passive seismic methods for crustal imaging in sparsely instrumented regions of intraplate West Africa.