The Klana Earthquakes of 1870 by Marijan Herak, Mladen Živci´ˇ C, Ivica Sovi´C, Ina Ceci´C, Iva Dasovi´C, Josip Stipcevi´ˇ C, and Davorka Herak INTRODUCTION
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○E Historical Seismicity of the Rijeka Region (Northwest External Dinarides, Croatia)—Part II: The Klana Earthquakes of 1870 by Marijan Herak, Mladen Živci´ˇ c, Ivica Sovi´c, Ina Ceci´c, Iva Dasovi´c, Josip Stipcevi´ˇ c, and Davorka Herak INTRODUCTION The wider epicentral region of Rijeka extends between Ilirska ABSTRACT Bistrica in Slovenia and Bakar in Croatia (Fig. 1). We have presented our work on three important historical events near The Klana earthquake sequence with the mainshock on 1 Bakar in the first part of the Rijeka area study (Herak et al., March 1870 (I max VIII Medvedev–Sponheuer–Karnik 2017), and here we shall investigate an important earthquake [MSK]) is one of the most important events that occurred of 1 March 1870, which devastated Klana, a small township ly- in the Rijeka (Croatia) epicentral region. It is remarkable ing some 15 km north-northwest of Rijeka (Fig. 1). At that time, notjustbecauseofitsimpacttothelocalcommunityand Klana was administratively in the district of Volosko of the Istria its significance for the seismic hazard in the Rijeka area County with the seat in Poreˇc, nowadays in Croatia. In 1870, but also because it provided some of important observations it was under the rule of the Austro-Hungarian Monarchy. on earthquake phenomena during the infancy of seismology. The Klana earthquake attracted much attention with the In particular, Stur (1871) seems to have been the first to contemporary general public and professionals alike. Newspapers attempt to explain the observed variation in damage by in- extensively reported on the events, commissions to investigate teraction of different local geological units during shaking; the damage were sent out to the epicentral area, and several de- Hoernes (1878) heavily relied on Stur’s data from the Klana tailed reports were written. An unprecedented amount of data epicentral region when he proposed that the vast majority regarding earthquake-related phenomena in these parts was col- of global earthquakes is related to the mountain-building lected in the field and documented by competent individuals and process and thus named them tectonic earthquakes.Despite was subsequently analyzed by the best geologists of the time. This this, the Klana earthquake so far has escaped any detailed collected material provided vital data in the study of the nature consideration by seismologists. In this study, we present of earthquake origin, and it was used (along with observations the historical data sources consulted to extract useful reports related to several other earlier earthquakes) by Hoernes (1878) on damage and other observed effects, compile macroseismic to propose his classification of earthquakes into cavity-collapse maps for the five strongest events, and invert the estimated events, volcanic earthquakes, and the most frequent ones: tec- intensity data to compute macroseismic hypocenters and tonic earthquakes. Stur (1871) performed the field investigations epicentral intensities for the mainshock and the two strongest around Klana that enabled him to attempt to explain observed aftershocks. We also present an earthquake chronicle with differences in damage as related to the local soil conditions. The data for 92 identified earthquakes in the area for the January– earthquake and its aftermath still attract historians and amateurs August 1870 period. The mainshock’smacroseismic (e.g., Šnajdar, 1997, who published elaborate accounts, analyzed epicenter is located near the active Rašafault–Klana-Novi some archive material). This event left a lasting impression and is Vinodolski fault system, which we thus propose to be the vividly remembered even today by the inhabitants of Klana: the primary source of the sequence. Macroseismic epicenters of mainshock occurred on Shrove Tuesday (Mardi Gras), and ever the aftershocks lie close to the surface trace of the nearby since all festivities in Klana related to the Shrovetide (Carnival) Skadanšˇcina-Rijeka reverse fault. officially end on Monday and not Tuesday (Šnajdar, 1997)! It is rather surprising that the strongest known event in the region that clearly plays an important role in hazard esti- Electronic Supplement: Earthquake chronicle and tables of mation of the large surrounding area and has profoundly localities, intensities, and sources. affected both the public and earthquake science has so far 1524 Seismological Research Letters Volume 89, Number 4 July/August 2018 doi: 10.1785/0220180064 Downloaded from https://pubs.geoscienceworld.org/ssa/srl/article-pdf/89/4/1524/4228925/srl-2018064.1.pdf by Istituto Nazionale di Geofisica e Vulcanologia INGV, Andrea Rovida on 07 February 2019.