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Can the Copy Fully Replace the Original: Fidelity of Legacy Seismic Data

Session: Back to the Future: Innovative New Research with Legacy Seismic Data

Type: Oral

Date: 4/19/2021

Presentation Time: 05:15 PM Pacific

Description: 

Over the long recording history of seismology, seismic data have been stored on many different types of media. Two of the most prolific among these are the original paper records and the corresponding microfiche with replicate seismograms. Today, there still exist large archives of both of these media, and it is highly likely that there exists overlap between these collections. Under the assumption that the microfiche records are exact duplicates of the original recordings, holders of paper collections may come under pressure to discard these bulky records in order to use the storage space for other purposes. However, before a decision can be made, it is necessary to understand what limitations exist for seismic data digitized from microfiche as opposed to from the original paper. While seismic data on microfiche can generally be recovered with similar fidelity to that on paper, we undertake a detailed comparison between corresponding records to note the existence of important differences. These arise mainly from distortion of the images, and the resolution and tonal-depth of scans. These effects can give rise to inaccuracies in the timing of records and in the recovery of data from large amplitude traces. Dependent upon the scientific problem, these issues can lead to misinterpretation. For example, the loss of information in the microfiche record indicate that earthquake signals with large undulations can become difficult to detect or digitize while they may be clearly perceptible in the paper version. Additionally, non-linear distortion in time may provide inaccurate timing of various phase arrivals and hence, inaccurate differential travel times with implications for topics like inner-core super-rotation. More broadly, when decisions regarding the allocation of resources for legacy data preservation efforts are made, it is crucial that the larger size and weight of the original paper records are balanced with the generally higher fidelity of data recoverable from these “master” copies of records.

Presenting Author: Thomas A. Lee

Student Presenter: Yes

Authors