Numerical Modeling of the Observed Wiechert Seismograph Magnification

Herak, Marijan; Allegretti, Ivo; Herak, Davorka; Duda, J. Seweryn

doi:10.1007/s000240050166

Cited by 8 publications

(3 citation statements)

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“…Based on the result shown by Herak et al (1996Herak et al ( , 1998, we may attribute such overestimation to a possible underestimation of the dynamic magnification of mechanical instruments operating in Italy and surrounding countries up to about the beginning of the 1960's. Hence, we could also suggest that in future calibrations of macroseismic magnitude relationships, the data of earthquakes that occurred before 1960 (when well calibrated electromagnetic seismometers started to be installed in Italy and all over the World) be excluded.…”

Section: Discussionmentioning

confidence: 90%

“…The dynamic magnification of the Wiechert seismometer at different frequencies can be calculated using a theoretical formula, whose validity was questioned by Herak et al (1996Herak et al ( , 1998 on the basis of a comparison with a modern seismometer installed for reference at the same site in Zagreb (Croatia). They found that the real magnification of the Wiechert seismometer installed at such site, at frequencies of interest for Ms computations (0.05 Hz), could be significantly underestimated by the theoretical formula by a factor of 2, producing an overestimation of Ms up to 0.3 m.u.…”

Section: Homogeneity Of Magnitudes Reported By the Cpti15 Catalogmentioning

confidence: 99%

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Inhomogeneity of Macroseismic Intensities in Italy and Consequences for Macroseismic Magnitude Estimation

Vannucci

Lolli

Gasperini

2021

Seismological Research Letters

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We show that macroseismic intensities assessed in Italy in the last decade are not homogeneous with those of the previous periods. This is partly related to the recent adoption of the European Macroseismic Scale (EMS) in place of the Mercalli–Cancani–Sieberg (MCS) scale used up to about one decade ago. The underestimation of EMS with respect to MCS is about a half of a degree on average and, even more significant, if the MCS intensities are estimated according to the approach developed for the quick evaluations of damage by macroseismic seismologists of the Italian Department of Civil Protection. We also show the inhomogeneity over time of the average differences between instrumental and macroseismic magnitudes computed from intensity data, indicating an average overestimation of magnitudes of about 0.3 units for the instrumental ones before year 1960 and of about 0.2 units for the macroseismic ones after such date. This is consistent with previous studies that hypothesized the incorrect calibration of mechanical recording seismometers operating in Italy and in the surrounding countries before the introduction of the standard electromagnetic seismometers from the beginning of 1960s. For such reasons, the magnitudes of preinstrumental earthquakes in the Catalogo Parametrico dei Terremoti Italiani seismic catalog, used for the most recent seismic hazard assessment in Italy, might be overestimated, on average, by about 0.1–0.2 magnitude units.

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Section: Discussionmentioning

confidence: 90%

Section: Homogeneity Of Magnitudes Reported By the Cpti15 Catalogmentioning

confidence: 99%

Inhomogeneity of Macroseismic Intensities in Italy and Consequences for Macroseismic Magnitude Estimation

Vannucci

Lolli

Gasperini

2021

Seismological Research Letters

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“…In order to carry out instrument response correction, the seismic traces have been corrected by specifying transfer function with the free period of pendulum (T o ), damping constant (h) and the magnification (V) of the instrument for mechanical sensors (Herak et al 1998). In fact, it is sometimes possible to find these values on the original seismograms even though it is a low possibility.…”

Section: The Instrument Response Correctionmentioning

confidence: 99%

Seismic parameters re-determined from historical seismograms of 1935-Erdek–Marmara Island and 1963-Çınarcık Earthquakes

2016

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In this study, the original seismograms of the 1935-Erdek-Marmara Island and 1963-Çınarcık Earthquakes, recorded at local and regional distances, were vectorized. The epicentral locations have been calculated using available readings from original records and also ISS and seismic station bulletins for 04.01.1935-14:41 and 16:20 Marmara Island-Erdek Earthquakes and 18.09.1963-16:58 Çınarcık Earthquake. The epicenter determinations show that the first event in 04.01.1935 was located at 40.72N-27.72E, while the second one occurred at 40.61N-27.43E, indicating that both were located near the Marmara Island. Another finding is that the 1963 event was located at 40.80N-29.18E, near the Princes' Island fault. Furthermore, moment tensor inversion method was applied on these earthquakes by using original seismograms, which provided an opportunity to illuminate the seismotectonic features of Marmara Region based on the retrieved fault mechanism solutions. For the first time, the fault mechanisms for 04.01.1935-14:41 and 16:20 Earthquakes were determined using moment tensor inversion from the original seismic waveforms. Likewise, the result obtained for the fault mechanism of 1963 Çınarcık Earthquake showed normal fault mechanism with much shallower depth than estimated before. Our preferred solutions showed that the fault mechanisms for the three events are normal faults and coincide with the seismotectonic structure of the Marmara Region.

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