Speaker
Mr
Remo Grolimund
(Swiss Seismological Service, ETH Zurich)
Description
Remo Grolimund, Evelyn Boesch, Donat Fäh
Swiss Seismological Service, ETH Zurich
ETH University Archives, ETH Zurich
**Seismicity in Switzerland in the early instrumental period
Re-assessment of the period 1911-1963 from a heterogeneous dataset**
After the compilation of the Swiss Earthquake Catalogue ECOS-091 the next logical step in the process of improving his¬torical earthquake information for Switzerland is the historical-critical revision of the seismicity of the period from 1878 to 1974. This is presently carried out in an interdisciplinary project funded by the Swiss National Science Foundation (2015–2019). The examined time span covers the pre-instrumental [1879– 1912] and early-instrumental period [1913–1963] of systematic scientific earthquake observation in Switzerland. The transitory period of 1964–1974, characterized by technical reconfigurations and a particular lack of documentation, has been adressed in an earlier project phase.
Due to the generally increased production of scientific data in this time range, we have the possibility for an in-depth analysis of a larger number of events with a sufficiently rich data base. To complete the investigations performed in the framework of ECOS-09 we can extend our focus to the intermediate-size events of epicentral intensities in the range IV–VI (in the European Macroseismic Scale EMS-98).
Whereas the documentation of the pre-instrumental period of systematic scientific earthquake observation by the Swiss Earthquake Commission SEC (1879/80–1912) can mainly rely on detailed macroseismic information3, the source situation gets more complex with the advent of instrumental observation and the establishment of the Swiss Seismological Service (SED) in 1912/14.
The assessment of this later period involves a multi-tiered analysis of a broad variety of sources containing both qualitative and quantitative data: descriptive reports and parameterized macroseismic information on the one side and historical seismograms and instrumental parameters on the other. This heterogeneous dataset is systematically gathered, archived and made accessible in this project. The large stock of historical seismograms a. o. recorded by a unique network of 3-component-Seismographs with pendulum masses of up to 21 tons and amplification factors of roughly 2000x is made accessible in a common sub-project with the ETH university archives. All events that have reportedly been felt whithin Switzerland are scanned in high resolution.
The early instrumental period provides us with a rich and diver¬se set of data that can be used to improve our understanding of seismicity and source-depth distributions as an important ele¬ment for future seismic hazard and risk assessments. Both in the case of the macroseismic as of the instrumental data we have extraordinarily long relatively homogeneous data sets at our disposal, as the relevant instrument settings and the inten¬sity scales in use remained unchanged during decades. Howe¬ver, both the macroseismic as the instrumental data show im¬portant gaps in tradition, due to neglective record keeping in the past and other factors. Used complementary, the different datasets may thus allow us to fill transmission gaps respecti¬vely. The datasets will allow cross-comparisons in further stu¬dies and can be used for calibration procdures.
The examination of the historical practice of data production and the comparison of this historical macroseismic dataset with macroseismic re-assessment in the modern EMS-98 scale can provide valuable insights for an empirical scale conversion. This may enable us to use the collected original intensities assessed in Rossi-Forel (for most of which primary data are lost) in the reconstruction of macroseismic fields.
Primary author
Mr
Remo Grolimund
(Swiss Seismological Service, ETH Zurich)
