**6.4 Evaluation of the different location methods**

At first we consider the epicenter solutions. **Figure 12** shows a representative sample of epicenter localizations by the six different methods (Kanamori,

*Seismological Data Acquisition and Analysis within the Scope of Citizen Science DOI: http://dx.doi.org/10.5772/intechopen.95273*

**Figure 12.**

*Epicenter solutions of 10 earthquakes in the southern half of the MSS-network: EQ23 is the acronym of the ML = 2.5 earthquake, 14th June 2019, addressed in Figures 3, 4, 5, and 11; triangles mark MSS-stations, gridline spacing of insert plots is 2 km.*

Apollonius, Geiger, Hyperbola, Hopkins, PS-circle) as described before. Subplots centered up the average of these epicenters show the particular solutions. Furthermore, the bulletin epicenters published by ZAMG (epi\_ZAMG) are included in the subplots. Generally, the four epicenters based on the travel-time data Tp and Tps (Geiger, Hyperbola, Hopkins, PS-circle) cluster together well. We calculate an average of these solutions (epi\_TpTps) and plot it on the map and the subplots. We also calculate the mean of the two epicenter solutions based on PGV data (Kanamori, Apollonius) and term it epi\_PGV.

The epicenter data compiled in **Figure 12** allow for a preliminary assessment of the accuracy of the solutions presented. We take epi\_TpTps as reference und calculate the lateral distances to the four travel-time based epicenter solutions (Geiger, Hyperbola, Hopkins, PS-circle), to epi\_PGV and to epi\_ZAMG. Statistical data about these differences are compiled in **Table 1**.

Disregarding outliers, the statistics compiled in **Table 1** indicates that the accuracy of epi\_TpTps (mean of epi\_Geiger, epi\_Hyperbola, epi\_Hopkins, epi\_PScircle) mimics the spacing of the search grid spacing (0.5 km). The accuracy of the bulletin solution (epi\_ZAMG) corresponds to the limitation to two decimals of longitude and latitude [0.01°] in the report.

Next, we consider the focal depth solutions for ten selected events. **Figure 13** shows the individual solutions gained by the six methods (Kanamori, Apollonius, Geiger, Hyperbola, Hopkins, PS-circle), the mean value of the travel-time based methods MSS\_TpTps, and the bulletin focal depth values from ZAMG. The bulletin solution fits to MSS\_TpTps for seven earthquakes in the Vienna Basin near the VBTF (Vienna BasinTransfer Fault) within the 1 km vertical spacing of the search grid. Foci at depths more than 3 km deeper than MSS\_TpTps are indicated by the

depth slices of the search grid at each optimum depth level for all methods. The visualization of the density of cell hits by Apollonius circles and PS-circles was applied for the corresponding methods. The hypocenter solutions differ not only between the methods based on the different data type, but also between the costfunction and cell-hit methods using the same data. The latter discrepancy is due to the different weighting of data by the cost function and cell-hit methods. Therefore the variance of the hypocenter solutions obtained by minimum-cost and cell-hit methods using the same data type may be an indicator of the accuracy or significance of the focal solution. The epicenter localizations of the sample earthquake by the six methods scatter within a circle with a radius of 1.6 km. The focal depth

*Location of the ML = 2.5 earthquake, 14th June 2019 by the (a) Kanamori, (b) Geiger, (c) Hopkins, (d) Apollonius, (e) hyperbola, and (f) PS-circle methods; depth slices through the search grids at the optimum focal depth levels are shown; data points (MSS-stations) and the extent of the search grid are marked; the cost function is shown for (a), (b), and (c), the cell-hit count for (e); Apollonius circles (d) and PS-circles (f)*

*Depth slices through the search grid visualizing (a), the cost function calculated by the Kanamori method and (b), the cell-hit count calculated by the hyperbola method; bright colors mark the cost function low and the cell*

At first we consider the epicenter solutions. **Figure 12** shows a representative

sample of epicenter localizations by the six different methods (Kanamori,

varies between 6 km and 8 km.

*visualize the corresponding focal solutions.*

**Figure 10.**

*Earthquakes - From Tectonics to Buildings*

*hit height.*

**Figure 11.**

**50**

**6.4 Evaluation of the different location methods**


been integrated into the development and production of the sensors, called

*Seismological Data Acquisition and Analysis within the Scope of Citizen Science*

network are principally accessible for the public.

*DOI: http://dx.doi.org/10.5772/intechopen.95273*

(https://www.macroseismicsensor.at/).

report their perceptions of ground motion.

**53**

'MacroSeismic Sensors' or MSS. The federal warning center of Lower Austria, local authorities, one quarry operator, and private people supported the selection and deployment of the MSS. We intentionally selected locations where citizens live or work and would be able report about felt ground motion. Up until October 2020 a total of 48 MSS were installed in our study area. All data collected by the MSS

Citizens willing to report on their perceptions of ground motion also want immediately to know about the source of their perceptions. Civil defense authorities need NRT information about the intensity and range of ground shaking for an instananeous organization of possibly necessary mitigation measures. Other authorities contacted are confronted with the problem of informing the public, within a few minutes of the event, about the impact of the seismic waves on people and infrastructure. We attempt to supply this information through the visualization of the MSS-network data on the internet in an intuitively ascertainable format. NRT observation of peak ground motion (PGV) at each MSS station is made possible by the visualization in a map (**Figure 3**). In case specific robust trigger criteria are met seismic data are defined as seismic events and archived. Some few seconds after the maximum amplitude seismic waves spread over the network area visualizations of the event PGV are available on internet. Interested parties and potential respondents (such as officials and civil protection personnel) are able to immediately assess the significance of the seismic event using the graphic facilities we offer

The correlation of instrumental data with intensity values based on reports about felt ground motions and their effect on infrastructure or nature is a general seismological issue and an essential task of our project. The conversion of PGV (or peak ground acceleration) into intensity or vice versa is fundamental for the just-in-

The integration of seismology in the curriculum at schools and in general is the third main goal of our project. So far, classes at polytechnic schools have produced several MSSs. They programmed the CNC-machine for the manufacturing of the mechanical parts and assembled the ADC board keeping electronic industry standard. Finally they assembled and tested the complete sensor. Another polytechnical class is still involved in programming of special add-on's for the visualization of the MSS data. During these courses, however, students focused more on general technical or technological skills (as the curriculum demanded) than on a deeper understanding of seismological phenomena. In order to compensate for this deficit we presented in this chapter elementary methods for seismic data analysis. These methods can be understood once principles in physics and mathematics at high school level are acquired. Despite the easy theoretical background of these methods, the simple amplitude-, or travel-time-distance relations, and computer codes, we determined locations and magnitudes of earthquakes in the area of the MSS network at an accuracy level comparable to the bulletin data of the ZAMG. We present our solutions on the homepage and citizens involved in the maintenance should be satisfied that their contributions to the installation and maintenance of the MSS network lead to results of scientific value. A further step could be a regional

time preparation of shake maps. So far, we have been able to correlate 120 macroseismic data points from 16 earthquakes with PGV data from the MSS network in the intensity range II – V. The correlation used by the Swiss Seismological Service for shake maps fits well with our relation at intensity V, but indicates higher PGV for the intensity range II – IV. We interpret this discrepancy as a commitment to extend our database in order to get a better knowledge of the correlation of PGV with intensity. Of course, we need the contribution of citizens, who are ready to

**Table 1.**

*Statistics of distances from epi\_TpTps to different epicenter solutions.*

#### **Figure 13.**

*Focal depth solutions for 10 events EQ3 – EQ42; dotted lines are the individual solutions determined by the six methods, solid blue line (MSS\_TpTps) is the mean of the travel-time based solution, solid red line focal depth solutions from the ZAMG-bulletin.*

bulletin for two earthquakes within the Northern Calcareous Alps. The focal depths resolved by the amplitude based methods (Kanamori and Apollonius) follow the trend of MSS\_TpTps but show systematically lower focal depths.

The locations by the Kanamori- and Apollonius methods include the determination of the magnitudes Eqs. 3, 4. We term the mean of both MSS\_M. This magnitude correlates well (correlation coefficient 0.96) with ML (bulletin magnitude, ZAMG). We derived the following relation:

$$\mathbf{M}\_{\rm L} = \mathbf{0}.\mathfrak{Y}\*\mathbf{M}\mathbf{S}\mathbf{S}\_{\rm M}\mathbf{M} \mathbf{-}\mathbf{0}.\mathfrak{Z}\mathfrak{G}\tag{17}$$

The difference between ML and MSS\_M could be explained by the constant C = �0.30 used by ZAMG in the local magnitude formula and not added to our magnitude calculation. The remainder may be caused by the difference in ground coupling between the MSS in buildings and the seismometers at observatories. The factor 0.97 instead of 1.00 may be due to the MSS frequency response limited by the 4.5 Hz geophones.

## **7. Conclusion**

A low-cost seismic sensor network has been installed in the southern Vienna basin, an area of moderate seismic hazard on a global scale, but high in Austria. Students of polytechnics in Wiener Neustadt (Lower Austria) and Vienna have

### *Seismological Data Acquisition and Analysis within the Scope of Citizen Science DOI: http://dx.doi.org/10.5772/intechopen.95273*

been integrated into the development and production of the sensors, called 'MacroSeismic Sensors' or MSS. The federal warning center of Lower Austria, local authorities, one quarry operator, and private people supported the selection and deployment of the MSS. We intentionally selected locations where citizens live or work and would be able report about felt ground motion. Up until October 2020 a total of 48 MSS were installed in our study area. All data collected by the MSS network are principally accessible for the public.

Citizens willing to report on their perceptions of ground motion also want immediately to know about the source of their perceptions. Civil defense authorities need NRT information about the intensity and range of ground shaking for an instananeous organization of possibly necessary mitigation measures. Other authorities contacted are confronted with the problem of informing the public, within a few minutes of the event, about the impact of the seismic waves on people and infrastructure. We attempt to supply this information through the visualization of the MSS-network data on the internet in an intuitively ascertainable format. NRT observation of peak ground motion (PGV) at each MSS station is made possible by the visualization in a map (**Figure 3**). In case specific robust trigger criteria are met seismic data are defined as seismic events and archived. Some few seconds after the maximum amplitude seismic waves spread over the network area visualizations of the event PGV are available on internet. Interested parties and potential respondents (such as officials and civil protection personnel) are able to immediately assess the significance of the seismic event using the graphic facilities we offer (https://www.macroseismicsensor.at/).

The correlation of instrumental data with intensity values based on reports about felt ground motions and their effect on infrastructure or nature is a general seismological issue and an essential task of our project. The conversion of PGV (or peak ground acceleration) into intensity or vice versa is fundamental for the just-intime preparation of shake maps. So far, we have been able to correlate 120 macroseismic data points from 16 earthquakes with PGV data from the MSS network in the intensity range II – V. The correlation used by the Swiss Seismological Service for shake maps fits well with our relation at intensity V, but indicates higher PGV for the intensity range II – IV. We interpret this discrepancy as a commitment to extend our database in order to get a better knowledge of the correlation of PGV with intensity. Of course, we need the contribution of citizens, who are ready to report their perceptions of ground motion.

The integration of seismology in the curriculum at schools and in general is the third main goal of our project. So far, classes at polytechnic schools have produced several MSSs. They programmed the CNC-machine for the manufacturing of the mechanical parts and assembled the ADC board keeping electronic industry standard. Finally they assembled and tested the complete sensor. Another polytechnical class is still involved in programming of special add-on's for the visualization of the MSS data. During these courses, however, students focused more on general technical or technological skills (as the curriculum demanded) than on a deeper understanding of seismological phenomena. In order to compensate for this deficit we presented in this chapter elementary methods for seismic data analysis. These methods can be understood once principles in physics and mathematics at high school level are acquired. Despite the easy theoretical background of these methods, the simple amplitude-, or travel-time-distance relations, and computer codes, we determined locations and magnitudes of earthquakes in the area of the MSS network at an accuracy level comparable to the bulletin data of the ZAMG. We present our solutions on the homepage and citizens involved in the maintenance should be satisfied that their contributions to the installation and maintenance of the MSS network lead to results of scientific value. A further step could be a regional

bulletin for two earthquakes within the Northern Calcareous Alps. The focal depths resolved by the amplitude based methods (Kanamori and Apollonius) follow the

*Focal depth solutions for 10 events EQ3 – EQ42; dotted lines are the individual solutions determined by the six methods, solid blue line (MSS\_TpTps) is the mean of the travel-time based solution, solid red line focal depth*

**Epicenter determination method Median Mean Maximum** Geiger, Hyperbola, Hopkins, and PS-circle 0.6 km 0.7 km 2.4 km epi\_ZAMG 0.8 km 1.0 km 2.0 km

1.9 km 3.0 km 6.9 km

epi\_PGV (mean of epicenter solutions gained by Kanamori and

*Statistics of distances from epi\_TpTps to different epicenter solutions.*

Apollonius method)

*Earthquakes - From Tectonics to Buildings*

**Table 1.**

**Figure 13.**

*solutions from the ZAMG-bulletin.*

The locations by the Kanamori- and Apollonius methods include the determination of the magnitudes Eqs. 3, 4. We term the mean of both MSS\_M. This magnitude correlates well (correlation coefficient 0.96) with ML (bulletin magnitude,

The difference between ML and MSS\_M could be explained by the constant C = �0.30 used by ZAMG in the local magnitude formula and not added to our magnitude calculation. The remainder may be caused by the difference in ground coupling between the MSS in buildings and the seismometers at observatories. The factor 0.97 instead of 1.00 may be due to the MSS frequency response limited by the

A low-cost seismic sensor network has been installed in the southern Vienna basin, an area of moderate seismic hazard on a global scale, but high in Austria. Students of polytechnics in Wiener Neustadt (Lower Austria) and Vienna have

ML ¼ 0*:*97 ∗ MSS\_M–0*:*36 (17)

trend of MSS\_TpTps but show systematically lower focal depths.

ZAMG). We derived the following relation:

4.5 Hz geophones.

**7. Conclusion**

**52**

initiative to supply volunteers with equipment to install and maintain a MSSstation, to perform their own data analysis aided by our computer programs, and to share "their" results with the community. We gladly support such initiatives.
