The Wood–Anderson of Trieste (Northeast Italy): One of the Last Operating Torsion Seismometers

Online Material: Earthquake catalog. The Wood–Anderson (WA) torsion seismograph, used by Richter (1935) for the definition of the local magnitude ( M L) of an earthquake, has been abandoned over time due to the cumbersome nature of its use. With the progress of technology, modern digital broadband (BB) instruments have replaced older instruments such as the WA, and the equivalent M L, obtained from simulated WA seismograms after convolution of the recorded BB data with a proper transfer function (Bormann, 2002a,b), has replaced the WA M L. Despite the paucity of WA instruments today, the M L in its original form remains relevant for continuity with old earthquake catalogs and as a long-standing reference for all other magnitude scales up to approximately M L 6.5. For larger earthquakes, the M L scale progressively underestimates the actual energy release and M L is said to saturate (Kanamori, 1983). Even so, M L is a good predictor of structural damage caused by earthquakes because many buildings have resonant periods close to that of the WA seismograph (0.8 s). In Trieste, located in northeastern Italy, there is one of the few stations equipped with an original pair of WA instruments that are still operating. The two horizontal WA seismometers (Lehner-Griffith TS-220) were installed in September 1971 and have been managed since then by the Osservatorio Geofisico Sperimentale, presently the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS). The Trieste station was part of the Worldwide Standardized Seismographic Station Network (WWSSN) with the code TRI-117, and it dates its operation back to 29 July 1963. At that time, three Benioff seismometers were employed as short-period seismographs, and three Ewing-Press seismometers …

[1]  Mark D. Semon,et al.  POSTUSE REVIEW: An Introduction to Error Analysis: The Study of Uncertainties in Physical Measurements , 1982 .

[2]  A. Saraò,et al.  The 1976 Friuli (NE Italy) thrust faulting earthquake: A reappraisal 23 years later , 2000 .

[3]  Acquiring, archiving, analyzing and exchanging seismic data in real time at the Seismological Research Center of the OGS in Italy , 2010 .

[4]  Walter H. F. Smith,et al.  New, improved version of generic mapping tools released , 1998 .

[5]  L. Peruzza,et al.  Probabilistic completeness assessment of the past 30 years of seismic monitoring in northeastern Italy , 2011 .

[6]  E. Hauksson,et al.  California Integrated Seismic Network (CISN) Local Magnitude Determination in California and Vicinity , 2011 .

[7]  H. O. Wood,et al.  Description and theory of the torsion seismometer , 1925 .

[8]  E. R. Collins,et al.  Synthesis of Wood-Anderson seismograms from broadband digital records , 1990 .

[9]  Göran Ekström,et al.  The global CMT project 2004–2010: Centroid-moment tensors for 13,017 earthquakes , 2012 .

[10]  P. Bragato,et al.  Local Magnitude in Northeastern Italy , 2005 .

[11]  P. Gasperini,et al.  The Italian CMT dataset from 1977 to the present , 2006 .

[12]  Nicholas Deichmann,et al.  Local Magnitude, a Moment Revisited , 2006 .

[13]  John H. Woodhouse,et al.  Determination of earthquake source parameters from waveform data for studies of global and regional seismicity , 1981 .

[14]  Silvia Castellaro,et al.  Regression problems for magnitudes , 2006 .

[15]  Hiroo Kanamori,et al.  Magnitude scale and quantification of earthquakes , 1983 .

[16]  H. Kanamori,et al.  A moment magnitude scale , 1979 .

[17]  R. Reyment,et al.  Statistics and Data Analysis in Geology. , 1988 .

[18]  P. Gasperini.  Local magnitude revaluation for recent Italian earthquakes (1981–1996) , 2002 .

[19]  C. Richter.  An instrumental earthquake magnitude scale , 1935 .

[20]  B. Romanowicz,et al.  Determination of local magnitude using BDSN broadband records , 1996, Bulletin of the Seismological Society of America.

[21]  P. Gasperini,et al.  Empirical Calibration of Local Magnitude Data Sets Versus Moment Magnitude in Italy , 2013 .

[22]  Dario Slejko,et al.  The 1976 Friuli (NE Italy) earthquake , 2005 .

[23]  A. Saraò,et al.  Fault-plane solutions from moment-tensor inversion and preliminary Coulomb stress analysis for the Emilia Plain , 2012 .