# Hazard Model: Epidemic-Type Aftershock Sequence (ETAS) Model for Hungary
## 2 Data  
The data quality requirements of an ETAS model fitting are challenging. A consistent instrumental earthquake catalogue for Hungary and the seismograph network collecting the measurements for this catalogue have only been in place since 1996 [19], and there has been a scarcity of significant Hungarian events from 1996 until 2022. For a sufficiently rich catalogue, the 2020 Zagreband the 2020 Petrinja, Croatia events and their aftershock sequences need to be included in the study. It is relevant to note that the Petrinja mainshock also caused damage and triggered insurance claims within Hungary [20]. These two event sequences have been recorded by the Hungarian seismograph network. On the other hand, both clusters fell largely outside the core geographical window of the Hungarian earthquake catalogue; this means that the study area is extended to the periphery of the data sources where the completeness and accuracy of data is less than optimal. Furthermore, large Croatian event sequences will have a dominant effect on the model fitting. The core geographical window of the study is the area between latitudes 45.5-49.0 N and longitudes 16.0-23.0 E. In order to include the Zagreb and Petrinja events, a margin to the west and to the south is added by defining the extended window as the area between latitudes 45.3-49.0 N and longitudes 15.7-23.0 E. The magnitude threshold of the study is set at \(M_{w}=2.5\). The data available for the study include both historical and recent instrumental data belonging to several Hungarian earthquake catalogues. These catalogues have been merged and event magnitudes have been homogenized to moment magnitude \(M_{w}\) for this study. Hereafter, the subscript \(w\) is omitted when referring to magnitudes. The component catalogues are the following (see also Figure 1):  
1. Catalogue A: Historical catalogue for the period 456 A.D. to 1995 [21], collected from several primary sources, partly instrumental and partly macroseismic. The number of events included in the extended window that reach the magnitude threshold is 2402. Due to obvious data quality limitations, these events are not used directly for ETAS parameter fitting but only as data for subsequent model downscaling. 2. Catalogue B: Instrumental catalogue covering the core window and the period 1996 to 2019, based on the recordings of the Hungarian seismograph network [19]. The number of events reaching the magnitude threshold is 654. 3. Catalogue C: Instrumental catalogue data for the period 1996 to 2010, collected and merged from international sources [22; 23; 24]. While some of the underlying sources are continuously updated, the merged dataset is only available to the end of 2010. The number of events included in the extended window that reach the magnitude threshold is 1107, partly overlapping with catalogue B data in the core window. 4. Catalogue X: Initial event list (IEL) data covering the period 2012 to 2021 [25], based on the recordings of the Hungarian seismograph network. IEL data are an interim phase of the yearly updates of the Hungarian instrumental earthquake catalogue (catalogue B). Geographical coverage is wider than the core window by a margin of 0.2 degrees latitude and 0.3 degrees longitude in all directions. Automated preliminary epicenter determinations are post-processed for the monthly publications of the list, which may result in some coordinate shifts across the window boundary. Thus, the western and southern edge of the extended window corresponds approximately to the geographical scope of the IEL. The number of events from IEL included in the extended window that reach the magnitude threshold is 2313, fully overlapping with catalogue B data in the core window in the period 2012 to 2019. Microseismic events caused by quarry blasts and explosions had been identified and excluded from the datasets during the preparation of the catalogues prior to this study. It is observed that the events in the Romanian area of the study show unusual magnitude-frequency patterns.