Some references:

https://link.springer.com/article/10.1023/A:1006364518204

https://www.ncbi.nlm.nih.gov/pubmed/8438739

I unfortunately don't have hands-on experience with SCG, so I don't know about the artifacts.

Seismocardiography (SCG)  is the registration of the mechanical consequence of the heartbeats, while ECG is the recording of the electrical activity associated with the activation of the myocardium. You can have the same electrical activation with different mechanical consequences...

SCG gives additional information about the quality of the ECG signals recorded: during phases of activity, the ECG signals are overlaid by artefacts from the activity. SCG serves to detect these phases, thus giving an indifation about the dependability of the ECG signals recorded.

Thank you all for your answers. I highly appreciate! :)