A Catalog of Old Spanish Seismographs

Abstract

For more than a century seismographs have been the main source of data for seismological research. Their design principles and performance have significantly changed from the early seismoscopes to the present broadband instruments. Knowledge of their characteristics and evolution is important in two ways. Firstly, the history and evolution of seismological research is closely linked to the progress in developing appropriate instrumentation. Secondly, accurate knowledge of the periods of operation and recording parameters of old instruments allows us to reanalyze their records on the basis of modern algorithms and theoretical concepts and thus to obtain new results on older 20th-century earthquakes (Kanamori, 1988). Additionally, seismographs can be considered as a materialized resume of the theoretical and technical knowledge in seismology at a given time. The study of their characteristics and evolution gives a deep insight into the roots and historical development of seismological science (Dewey and Byerly, 1969 ; Ferrari, 1997). Some seismographs have been designed and constructed by eminent seismologists, and some seismologists got their reputation because they constructed good seismographs. The second objective is not an easy one. In the late 1950's and early 1960's, the global introduction of highly sensitive electrodynamic sensors with galvanometric photographic or electronically amplified recordings on paper or tape outdated almost every available instrument up to that time. The most conspicuous exponent, but not the only one, of that change was the deployment of the World Wide Standard Seismograph Network (WWSSN), which resulted in much more homogeneous global data coverage, significantly lowered detection thresholds, and improved earthquake location and catalog completeness. As a result, significant improvement of global seismicity patterns and understanding of their relationship to global plate tectonics, velocity models, and many other important seismological findings arose. But the real breakthrough came only in the 1980's and 1990's with the development …