Abstract
In this study, we analyzed the near-field seismic records of two moderate sized earthquakes in the Western Balkan region: the September 2016 Skopje earthquake, magnitude ML5.3 and the March 2020 Zagreb earthquake, magnitude ML5.5. Such recordings at close epicentral distances are rare and are thus very useful for testing some of the theoretical assumptions used in modeling earthquake risk. Firstly, response spectra were computed using the digital time histories for the three closest stations to the Skopje 2016 earthquake and the two closest stations to the Zagreb 2020 earthquake. Their characteristics were examined in terms of frequency and peak amplitude ranges. Secondly, the Nakamura method was applied to the records from the selected five stations coded SKO, FCE, IZIIS, QUHS, and QARH. The results of the spectral analysis were compared with interpretations from the geological and geotechnical maps at each location. Our findings support the idea that these combined methods can be used to categorize the underlying structural profile to a first approximation and can be used to derive velocity models.
Highlights
On 11 September 2016 at 13:10 UTC time a strong, magnitude ML 5.3, earthquake occurred under the Macedonian capital Skopje
The stations’ location and the epicenter superimposed over the geology map of the Zagreb region are displayed on Figure 2
There was a lack of instrumental data at short distance during the 1963 Skopje earthResponse spectra for the Zagreb event showed the peak values mainly between 0.1 quake and compiled reports were mainly based on macroseismic data depicting intensity, and 0.2 s, equivalent to frequencies of 5–10 Hz, that corresponds with observed building the 2016 earthquake was recorded at several local and regional seismic stations
Summary
On 11 September 2016 at 13:10 UTC time a strong, magnitude ML 5.3, earthquake occurred under the Macedonian capital Skopje. Using data from the local and regional seismic stations, the UKIM Seismological Observatory SKO estimated its location at 42.008◦ N and 21.488◦ E [1,2]. Global seismic records favored a shallow focal depth of about 10 km [3] Such tremors create panic among residents because the Skopje region has a history of strong and damaging earthquakes. The maximum felt intensity was VII-VIII (MSK scale), causing one death and injuring 27 people It was the strongest earthquake in the Zagreb area in the last 140 years and caused substantial damage in the historical town center. March earthquakes recorded onthe the from the Skopje September 2016 and Zagreb March 2020 earthquakes recorded on closest stations and apply the Nakamura method and discuss the results in the closest stations and apply the Nakamura method and discuss the results in the context context of the existing geological maps at each site. The stations’ location and the epicenter superimposed over the geology map (detailed explanation in [7]) of the Zagreb region are displayed on Figure 2
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