Annals 48, 2, 2005defdef 215 ANNALS OF GEOPHYSICS, VOL. 48, N. 2, April 2005 Key words Mt. Etna – local magnitude – volcano seismicity 1. Introduction In order to know the size of an earthquake without considering the produced effects, Richter proposed the definition of magnitude and related it to the maximum amplitude of the ground dis- placement. The «local magnitude» ML (Richter, 1935), is defined with the relationship log logM A AL 0= - where A is the maximum amplitude peak to peak measured in mm, recorded by a standard Wood- Anderson seismometer with natural period of 0.8 s, magnification 2800 and damping factor 0.8. The quantity «−logA0» is defined empirical- ly with respect to a reference earthquake, which describes the variation of maximum amplitude (A) of the event related to the epicentre distance (∆). Geometric spreading, elastic attenuation and scattering of seismic waves, therefore, influ- ence the amplitude decay. Richter fixed A0 (∆) level at 1 µm for a distance of 100 km. Later, to evaluate magnitude in a more prac- tical approach, principally when the recording of strong earthquakes is clipped in amplitude, em- piric relationships were developed using the du- ration of the seismic event by Solov’ev (1965), Tsumara (1967) and many other authors. In the last twenty years, earthquake magni- tudes were always estimated at Mt. Etna vol- cano with the duration of the seismic event us- ing appropriate relationships. Caltabiano et al. (1986), used the Serra Piz- zuta Calvarina (ESP) station of Permanent Seis- mic Network run by Istituto Internazionale di Vulcanologia (IIV) of the CNR of Catania, for the following relationship: . . .log logM 1 367 2 068 0 212D = - + +x ∆ Local magnitude estimate at Mt. Etna Salvatore D’Amico and Vincenza Maiolino Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania, Italy Abstract In order to verify the duration magnitude MD we calculated local magnitude ML values of 288 earthquakes oc- curring from October 2002 to April 2003 at Mt. Etna. The analysis was computed at three digital stations of the permanent seismic network of Istituto Nazionale di Geofisica e Vulcanologia of Catania, using the relationship ML = logA+ alog∆ − b, where A is maximum half-amplitude of the horizontal component of the seismic record- ing measured in mm and the term «+ alog∆ − b» takes the place of the term «− logA0» of Richter relationship. In particular, a = 0.15 for ∆ < 200 km, b = 0.16 for ∆ < 200 km. Duration magnitude MD values, moment magnitude MW values and other local magnitude values were compared. Differences between ML and MD were obtained for the strong seismic swarms occurring on October 27, during the onset of 2002-2003 Mt. Etna eruption, charac- terized by a high earthquake rate, with very strong events (seismogram results clipped in amplitude on drum recorder trace) and high level of volcanic tremor, which not permit us to estimate the duration of the earthquakes correctly. ML and MD relationships were related and therefore a new relationship for MD is proposed. Cumula- tive strain release calculated after the eruption using ML values is about 1.75E + 06 J1/2 higher than the one cal- culated using MD values. Mailing address: Dr. Salvatore D’Amico, Istituto Nazio- nale di Geofisica e Vulcanologia, Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy; e-mail: damico@ct.ingv.it 216 Salvatore D’Amico and Vincenza Maiolino where τ is the duration time of the event in sec- onds and ∆ is hypocentre distance in km. These authors studied a dataset of 70 earth- quakes with hypocentre distance within 11 km for an extremely local relationship. The differ- ence between P- and S-waves arrival time was used to estimate the hypocentre distance. Istitu- to Nazionale di Geofisica e Vulcanologia (IN- GV) supplied the reference magnitude. Later, Cardaci and Privitera (1996) intro- duced a new relationship to calculate duration magnitude for the permanent seismic network of IIV, based on methodology proposed by Real and Teng (1973). The dataset analysed by the au- thors was composed of 198 earthquakes record- ed between 1990 and 1994, the reference magni- tude, supplied by Istituto Nazionale di Geofisica e Vulcanologia, is comprised between 2.0 and 3.5 and was estimated on stations far from Mt. Etna using the duration of event recording. 2. Magnitude of Mt. Etna earthquakes At present the Mt. Etna Permanent Seismic Network, of the Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania (INGV-CT), consists of 30 stations. The seismic signals are acquired continuously and are transmitted via ra- dio to Centro Acquisizione Dati Sismici (CADS) of the INGV-CT where they are digitally saved with a sampling rate of 125 Hz. As routine, the magnitude of earthquakes recorded by the Permanent Seismic Network of (INGV-CT) is calculated using the duration of the seismic event recorded on a drum recorder using the relationship of Caltabiano et al. (1986). The reference station was ESP until 1999 and there- after EMA. Usually, when an event is «truncated» by the occurrence of another seismic event, the du- ration is estimated by amplitude decay. Recent seismic swarms, which occurred dur- ing the opening of the eruptive fractures of the last eruptions (2001 and 2002-2003), were char- acterized by a high earthquake rate, with very strong events (seismogram results clipped in am- plitude on drum recorder trace) and high level of volcanic tremor. Figure 1 shows the seismogram of the seismic swarm during the onset of 2002- 2003 Mt. Etna eruption. From 00:27 GMT of 27.10.2002, it was very difficult to estimate the Fig. 1. Seismogram at EMA station recorded between 26.10.2002 at 23:30 GMT and 27.10.2002 at 00:59 GMT. 217 Local magnitude estimate at Mt. Etna duration of each earthquake and the related mag- nitude. In order to verify the duration magnitude calculated for the earthquakes of 2002-2003 Mt. Etna eruption, we worked to simulate a Wood- Anderson seismometer and then computed local magnitude with the relationship (Lahr, 1999) log logM A a bL = + -∆ where A is maximum half-amplitude of the hor- izontal component of the seismic recording measured in mm and the term «+ alog ∆ − b» takes the place of the term «−logA0» of Richter relationship. In particular, a = 0.15 for ∆ < 200 km, b = 0.16 for ∆ < 200 km. The approxima- tion for this parametric form is smaller than 0.2 in comparison with correction values for source-receiver distance from Richter’s table (Di Grazia et al., 2001). ∆ is hypocentre dis- tance in km and is calculated by the relationship D H Q 2 2 = + +∆ ^ h where D is epicentre distance in km, H is the depth of the earthquake in km b.s.l. and Q is the altitude of the station in km a.s.l. 3. The 2002-2003 Mt. Etna eruption In the night between October 26 and 27, 2002 a seismic swarm occurred in the central upper part of Mt. Etna. It was the start of a new eruption of Etna that formed fissures on both the NE and S flanks of the volcano. On October 27 eruptive fissures opened on the higher flank of the volcano produced high fire fountains, evolving into ash columns (Calvari et al., 2004). On October 29, numerous tectonic structures on the eastern flank of the volcano were activated through seismic swarms, causing serious damage to S. Venerina village and in the neighbouring areas on Mt. Et- na’s eastern flank (Azzaro and Mostaccio, 2003; Azzaro and Scarfì, 2003). The eruption gave rise to a huge lava emis- sion from both fracture fields and powerful ex- plosive activity from the southern one. After 94 days the eruption ended on January 28, 2003. Much of the seismicity occurred during the first day of the eruption, while the remarkable clusters of earthquakes on the southeastern flank are largely related to the 29 October seismic crisis. An overall number of 862 earthquakes (MD ≥ ≥1) were recorded by the permanent seismic network run by INGV-CT. Maximum magni- tude observed was 4.4 and 56 earthquakes ex- ceeded MD = 3.0. 4. Data analysis The dataset used in this work is composed of 288 earthquakes occurring between October 2002 and April 2003 (fig. 2). The magnitude (MD) of these earthquakes is between 1.0 and 4.4. The fo- cal depths of the earthquakes are concentrated within the uppermost 5 km below sea level (b.s.l.). To study the relationship for the local mag- nitude we used the digital stations ESP, EMV and EMG. The first is equipped with a Lennartz LE-3D/20s seismometer; the others (EMV and EMG) are equipped with Lennartz LE-3D/1s sensors. The former is a broadband seismome- ter with corner frequency ω 0 = 0.05 Hz (20 s), output voltage k = 1000 V/m/s and damping h = = 0.707; the LE-3D/1s have a corner frequency ω 0 = 1.00 Hz, output voltage k = 400 V/m/s and damping h = 0.707. Fig. 2. Mt. Etna map. The grey squares indicate the stations used to calculate the local magnitude (ML) or the duration magnitude (MD). The earthquakes epicen- tres are indicated with crosses; earthquakes occurring on October 26 and 27, 2002 are indicated with asterisks. 218 Salvatore D’Amico and Vincenza Maiolino The errors on the epicentre and hypocentre coordinates are smaller than 2 km. 4.1. Methodology For each selected earthquake (fig. 3a), we cal- culated a Discrete Fourier Transformation (DFT) on the horizontal components of the seismic re- cord (fig. 3b). The velocity response curve of the seismometer (fig. 3c) is defined by the relation- ship - ~ ih k E 20 2 2 0 2 = + ~ ~ ~ ~ ~ ] ^ g h where k is the sensitivity of the transducer in V/m/s, ω is the angular frequency, ω 0 is the nat- ural period, and h is the damping. This kind of Table I. One-dimensional VP velocity model. Top layer (km) VP velocity (km/s) 0.00 3.00 0.50 3.59 2.00 4.00 4.00 4.80 6.00 5.59 12.00 6.50 30.00 8.00 Fig. 3a-h. The DaDisp worksheet used to simulate a seismic signal recorded by standard Wood-Anderson seis- mometer. a) Velocity seismic signal recorded by geophone; b) DFT of velocity seismic signal; c) velocity re- sponse curve of geophone; d) displacement response curve of geophone; e) Wood-Anderson response curve; f) velocity spectrum divided by displacement response curve; g) corrected spectrum multiplied by Wood-Ander- son response curve; h) Wood-Anderson simulated seismic signal. Analytic locations of the earthquakes were performed by HYPOELLIPSE routine (Lahr, 1999), using a onedimensional VP velocity model with 7 plane-parallel layers (Hirn et al., 1991) as de- scribed in table I. a b c d e f g h 219 Local magnitude estimate at Mt. Etna sensor has no calibration coil and it is very diffi- cult to know the real technical parameters, for this reason we used the data reported in the fac- tory datasheet. Velocity response curve was transformed in displacement response curve (fig. 3d), by mul- tiplying it for the angular velocity ω (Bath, 1974) before correcting the velocity spectrum. Multiplying the response curve of a standard Wood-Anderson seismometer (fig. 3e), with static magnification 2800, damping 0.8 and nat- ural period 0.8 s (Richter, 1935), with the correct displacement spectrum (fig. 3f) we obtained sig- nal of fig. 3g. The simulated Wood-Anderson seismogram (fig. 3h) was obtained with DFT in- verse of fig. 3g. We used the software DaDisp 4.0 to analyse the digital signals on the whole seismic record. The half-amplitude A, used to obtain the magni- tude, was calculated as a mean of N-S and E-W components. Urhammer and Collins (1990), verified that the 2800 static magnification is determined by the manufacturer and it is not the static magni- fication determined from measurements of the natural period and tilt-sensitivity. They suggest using the value of approxi- mately 2080. Assuming a static magnification of 2800 (as has been common practice, e.g., Bakun et al., 1978; Kanamori and Jennings, 1978; Lu- co, 1982; Del Pezzo and Petrosino, 2001) will lead to a systematic over estimation of ML by an average of 0.13 ML units (Urhammer and Collins, 1990). We decided to apply the 2800 static magni- fication value to this work because it is more widely used in common practice and the calcu- lated ML is comparable with ML calculated from stations of different networks. 5. Results 5.1. Comparison with duration magnitude Figure 4 shows the magnitude values ML calculated at ESP compared with the corre- sponding magnitude values MD. The grey squares indicate earthquakes occurring between October 26 and 27. MD values are overestimat- ed respect to ML and are scattered for about 1.0 units on MD axis below ML = 2.2. This data scat- tering is due to error on estimate of earthquake duration. Moreover, grey squares dataset shows a different trend with respect to white squares dataset. Fig. 4. Comparison between MD and ML at ESP station. The grey squares indicate the earthquakes occurring from October 26 at 00:27 GMT and October 27; the thick black line of linear regression and relative equation refers to white squares dataset. 220 Salvatore D’Amico and Vincenza Maiolino A linear regression between MD and ML val- ues was performed, excluding the October 26 and 27 dataset. The relationship obtained is . .M M0 6668 1 008D L= + with coefficient of variation of the regression R2 = 0.7737. Figure 5 shows the magnitude ML (at ESP station) with respect to time origin. Earth- quakes with higher magnitude were recorded Fig. 6. Difference MD − ML (at ESP station) with respect to time origin. The grey squares indicate the earth- quakes occurring on October 26 at 00:27 GMT and October 27. Fig. 5. ML calculated at ESP station with respect to time origin. The grey squares indicate the earthquakes oc- curring on October 26 at 00:27 GMT and October 27. 221 Local magnitude estimate at Mt. Etna during the opening of the eruptive fractures (October 26 and 27, grey squares), while the earthquakes with the smaller magnitude were recorded only at the end of the eruption. We may assume that the estimate of the magnitude MD on October 26 and 27 is not per- fectly correct. In fact, as mentioned above, when there are many earthquakes in a short time, or when there is higher amplitude of the volcanic tremor, it is more difficult to read the real dura- tion of the earthquake. Moreover, the strongest earthquakes recorded on the drum recorder, show clipped amplitude (see fig. 1). For these reasons it is very difficult to estimate the ampli- tude decay. This amplitude saturation infers on- ly the trace drawn by the drum recorder pen and it does not affect the digitally recorded signal. This theory is in agreement with fig. 6, where the difference MD − ML (at ESP station) with respect to time origin is shown. The graph again highlights MD higher than ML except for earthquakes on October 26 and 27, 2002. Fig- ure 7 compares the ML values, at EMG and EMV, with ML values at ESP; there is a good agreement between ESP and EMG values; the EMV values have a good agreement above ML > > 1.5, but are overestimated by about 0.5. Figure 8a,b shows velocity and Wood-Ander- son simulated traces of two seismic events. The signal-noise ratio at EMV station is smaller than other two stations, both during the eruptive phase (fig. 8a), with a high level of volcanic tremor, and at the end of the eruption (fig. 8b). We think that EMV values are affected by site-effect overestimating magnitude values with respect to ESP and EMG values. This site- effect is more evident for earthquakes with ML >1.5, while for the other earthquakes the signal-noise ratio at EMV station is very small and it is not possible to estimate the maximum amplitude peak to peak clearly. Following Gasperini (2002), we proceeded to a calibration of a new relation of MD on the basis of the dataset of ML magnitudes excluding the Octo- ber 26 and 27 earthquakes, and of the duration val- ues. In our analysis we computed the coefficients of a linear regression, equivalent to the Caltabiano et al. (1986) formula, of ML with both logτ and log∆ as independent variables. This gives ( . . ) ( . . ) ( . . ) log log M 2 477 0 099 0 464 0 172 2 655 0 227 L ! ! ! = + + - x ∆ with coefficient of variation of the regression R2 = 0.770. The linear regression computed is neverthe- less affected by errors on duration estimate. In order to reduce the errors in the coefficients we performed another linear regression excluding data with residuals obtained from previous re- Fig. 7. Relation between ML estimated at EMG station (white), at EMV station (grey) and at ESP station. 222 Salvatore D’Amico and Vincenza Maiolino Fig. 8a,b. 27.10.2002 at 05:46 GMT (a) and 03.03.2003 at 13:42 GMT (b) events recorded at ESP, EMV and EMG station. Left: traces acquired by seismic station in velocity; right: Wood-Anderson simulated traces. Fig. 9. Relation between Moment magnitude MW (white squares), local magnitude (Mbb) at broadband stations of MedNet (black squares), duration magnitude MD (grey triangles) calculated with the new relation and local magnitude ML at ESP station. a b 223 Local magnitude estimate at Mt. Etna gression greater of 0.25 units. The result is ( . . ) ( . . ) ( . . ) log log M 2 494 0 073 0 438 0 131 2 644 0 176 L ! ! ! = + + - x ∆ with coefficients of variation of the regression R2 = 0.873. 5.2. Comparison with magnitude values calculated using different methods Figure 9 plots MD values obtained from the new Duration-Magnitude scale (grey triangles) versus ML values. We also compared the local magnitude values estimated by the broadband stations of MedNet seismic network located in Sicily (black squares) and the moment magni- tude estimated by seismic moment (white squares). The magnitude (Mbb) is calculated using the Richter relationship (1935) as a mean value from the horizontal components of the AIO and VAE stations (MEDNET, 2003). The moment magnitude (MW) is calculated with Kanamori’s relationship (Lay and Wallace, 1995) . . log M M 1 5 10 73W 0 = -c m where M0 (Keilis-Borok, 1957) is seismic mo- ment obtained by source parameters (Brune, 1970) at station ESP (Giampiccolo et al., 2003). A good agreement is shown between ML values and new MD values. Moreover, we ob- serve that, with a few exceptions, Mbb values agree with ML values, and MW values agree with ML values for ML > 2.7. 6. Strain release Figure 10 shows the cumulative strain re- lease (Joule1/2) calculated by MD (thin line) and by ML values (thick line). The strain release value of the earthquake was obtained as the square root of the energy E in Erg, which is es- timated with Richter’s relationship (1958) Fig. 10. Cumulative energy strain release in the period October 14, 2002-April 5, 2003. Thin line represents strain release calculated by MD values, while thick line represents strain release calculated by ML values. Dark grey area highlights October 27 day and light grey area the eruptive period (October 28, 2002-January 27, 2003). 224 Salvatore D’Amico and Vincenza Maiolino . . .log E M M9 9 1 9 0 024 2 = + - for M ≤ 4.5 . .log E M11 8 1 5= + for M > 4.5 where M is the magnitude. In the figure two periods are highlighted: the former (dark grey) indicates the seismic swarm occurring on October 27, corresponding to the opening of the eruptive fractures, while the lat- ter (light grey) represents the eruption beginning on October 28 and ending on January 27. A marked difference of cumulative strain re- lease between MD and ML series is observable during the seismic sequence of October 27, due to the underestimated MD values as seen in figs. 4 and 6. In the later period, where it is easier to estimate the duration of the earthquakes, the strain release values are comparable. After the eruption the overall difference of strain release calculated from ML values and from MD values is about 1.75E + 06 J1/2. 7. Conclusions The aim of this work was to estimate local magnitude by simulating a Wood-Anderson seis- mometer and compare the results with different magnitude scales. ML values calculated at ESP and EMG are ab- solutely coherent, while EMV values are overes- timated by 0.5. ML values compared with Mbb and MW val- ues show a good correlation. MD values seem to be overestimated. Al- though it is difficult obtaining reliable MD values with this dataset for the strongest earthquakes, corresponding to the opening of the eruptive fracture a try to recognise a relationship between ML and MD was performed. A new duration-mag- nitude scale is proposed. The dataset used and the ML values calcu- lated are reported in the Appendix. In conclusion, it is remarkable that in envi- ronments with high seismic noise, such as Mt. Etna volcano, the magnitude estimates based on the measurement of the ground amplitude are more reliable and that some care must be taken in using a magnitude scale based on coda dura- tion for low values of magnitude when the noise level is high. As the correct estimate of seismic parameters is important for a quantitative eval- uation of volcano dynamics, the Wood-Ander- son magnitude scale should be routinely deter- mined together with duration-magnitude in vol- cano monitoring. A software program to reach these objectives is in preparation at this time. Acknowledgements We are grateful to F. Mulargia and S. Castel- laro for their constructive criticism that strong- ly improved the early version of this paper. 14.10.2002 03.34.14 2.6 2.0 14.10.2002 03.55.16 2.6 1.8 14.10.2002 04.40.30 2.1 1.9 15.10.2002 21.22.13 2.0 1.8 16.10.2002 10.10.21 1.5 1.2 17.10.2002 19.28.58 2.1 1.5 17.10.2002 19.41.44 1.5 1.6 18.10.2002 04.04.15 2.1 2.1 Appendix. Dataset used for the analysis and ML values. Time Origin MD ML Time Origin MD ML 18.10.2002 04.06.29 1.9 1.7 18.10.2002 04.47.12 1.7 1.6 22.10.2002 01.39.07 2.1 1.8 22.10.2002 16.29.15 2.5 2.3 26.10.2002 21.35.54 2.4 1.8 26.10.2002 21.46.51 2.3 1.6 26.10.2002 21.55.39 2.4 1.6 26.10.2002 22.04.57 2.4 1.4 225 Local magnitude estimate at Mt. Etna 26.10.2002 22.17.57 2.3 1.6 26.10.2002 22.25.38 2.5 1.8 26.10.2002 22.28.25 2.4 1.9 26.10.2002 22.33.40 2.4 2.2 26.10.2002 22.40.45 2.5 2.2 26.10.2002 22.51.16 2.5 2.0 26.10.2002 23.13.08 2.4 2.2 26.10.2002 23.22.29 2.7 2.7 26.10.2002 23.27.48 2.4 1.8 26.10.2002 23.30.22 2.4 1.7 26.10.2002 23.46.34 2.4 2.0 26.10.2002 23.49.42 2.4 1.8 27.10.2002 00.12.57 2.3 1.4 27.10.2002 00.13.19 2.6 2.6 27.10.2002 00.13.29 3.0 2.8 27.10.2002 00.16.45 2.7 2.9 27.10.2002 00.21.11 2.4 2.1 27.10.2002 00.21.51 2.7 2.5 27.10.2002 00.23.49 2.5 2.4 27.10.2002 00.26.29 2.5 3.0 27.10.2002 00.29.39 3.1 3.4 27.10.2002 00.30.39 3.2 2.8 27.10.2002 00.32.38 2.9 3.7 27.10.2002 00.34.12 3.1 3.4 27.10.2002 00.35.03 3.0 3.3 27.10.2002 00.36.09 3.1 2.4 27.10.2002 00.41.49 3.2 3.9 27.10.2002 01.01.40 2.7 2.9 27.10.2002 01.07.46 2.4 3.1 27.10.2002 01.08.18 2.6 3.3 27.10.2002 01.11.25 3.0 3.5 27.10.2002 01.13.32 3.3 3.9 27.10.2002 01.23.48 3.0 3.8 27.10.2002 01.26.24 3.0 3.3 27.10.2002 01.28.17 3.5 4.1 27.10.2002 01.29.27 2.7 3.1 27.10.2002 01.30.30 2.8 3.3 27.10.2002 01.33.24 2.6 2.7 27.10.2002 01.34.25 2.4 2.6 27.10.2002 01.36.13 2.4 3.0 27.10.2002 01.37.11 2.6 3.0 27.10.2002 01.38.28 2.8 3.4 27.10.2002 01.42.21 2.7 3.3 27.10.2002 01.53.01 2.5 3.2 27.10.2002 02.15.17 2.5 3.4 27.10.2002 02.18.29 3.2 3.9 27.10.2002 02.29.28 3.5 4.0 27.10.2002 02.39.10 3.3 4.0 27.10.2002 02.42.11 3.4 4.2 27.10.2002 03.18.15 2.8 2.2 27.10.2002 03.28.55 2.8 3.5 27.10.2002 03.53.26 2.5 3.3 27.10.2002 04.13.12 2.4 3.1 27.10.2002 04.17.07 2.9 3.8 27.10.2002 05.02.04 2.5 3.1 27.10.2002 05.20.57 2.6 3.2 27.10.2002 05.25.05 2.6 3.5 27.10.2002 05.31.11 3.3 4.2 27.10.2002 05.46.45 3.4 3.9 27.10.2002 06.06.55 3.4 3.4 27.10.2002 06.26.13 2.8 3.3 27.10.2002 06.28.14 2.9 3.8 27.10.2002 06.49.32 2.9 3.8 27.10.2002 07.32.06 3.2 4.4 27.10.2002 08.04.32 2.8 3.4 27.10.2002 10.07.56 2.7 3.3 27.10.2002 10.24.48 2.7 3.4 27.10.2002 11.03.01 2.6 3.2 27.10.2002 12.09.58 2.7 2.9 27.10.2002 12.16.05 2.6 3.0 27.10.2002 12.44.21 2.3 3.1 27.10.2002 13.23.56 2.7 3.3 27.10.2002 13.34.56 2.6 3.3 27.10.2002 14.00.44 2.7 3.8 27.10.2002 14.42.44 2.5 3.1 27.10.2002 14.56.29 2.7 3.4 27.10.2002 15.51.07 3.0 3.8 27.10.2002 15.56.17 2.8 3.2 27.10.2002 16.02.09 2.9 3.2 27.10.2002 16.07.46 2.6 2.9 Appendix (continued). Time Origin MD ML Time Origin MD ML 226 Salvatore D’Amico and Vincenza Maiolino 27.10.2002 16.47.50 2.7 3.1 27.10.2002 22.04.17 2.6 2.8 28.10.2002 03.01.40 3.2 4.0 28.10.2002 09.12.37 3.2 2.8 28.10.2002 11.40.10 3.1 3.2 28.10.2002 11.51.32 2.8 3.0 28.10.2002 16.27.04 3.0 3.2 28.10.2002 23.25.47 2.0 1.8 29.10.2002 01.31.46 2.6 2.7 29.10.2002 02.32.48 2.3 1.8 29.10.2002 07.22.33 2.6 2.4 29.10.2002 07.27.14 2.6 2.0 29.10.2002 08.34.33 2.9 3.5 29.10.2002 09.56.49 2.0 1.8 29.10.2002 10.02.09 3.0 2.8 29.10.2002 10.02.20 4.4 3.7 29.10.2002 10.04.41 3.1 3.1 29.10.2002 10.12.51 2.4 2.3 29.10.2002 10.13.25 2.8 2.8 29.10.2002 10.17.37 2.5 2.5 29.10.2002 10.18.48 2.1 2.2 29.10.2002 10.34.58 2.9 2.9 29.10.2002 10.56.09 3.6 3.5 29.10.2002 10.59.42 2.1 2.0 29.10.2002 11.02.00 4.0 3.4 29.10.2002 11.20.06 1.9 1.6 29.10.2002 11.22.04 1.7 1.5 29.10.2002 11.32.42 1.9 2.2 29.10.2002 11.51.40 2.7 2.3 29.10.2002 12.21.57 2.1 2.2 29.10.2002 13.25.31 2.7 2.7 29.10.2002 15.49.50 3.8 3.6 29.10.2002 16.39.46 4.0 4.1 29.10.2002 17.14.00 4.1 3.5 29.10.2002 19.07.48 1.7 1.6 29.10.2002 20.35.16 2.0 1.7 29.10.2002 22.24.47 2.8 2.4 30.10.2002 00.00.13 3.1 2.9 30.10.2002 02.16.17 2.0 2.1 30.10.2002 02.20.28 2.5 2.5 30.10.2002 07.20.06 2.5 1.8 30.10.2002 10.05.38 2.2 2.0 30.10.2002 10.06.23 2.5 1.8 30.10.2002 10.47.00 2.6 2.4 30.10.2002 15.25.43 3.2 3.3 30.10.2002 15.38.37 2.6 2.5 30.10.2002 21.13.20 1.9 1.6 30.10.2002 21.14.42 2.5 2.1 30.10.2002 21.15.03 2.1 1.7 30.10.2002 21.17.35 1.7 1.7 30.10.2002 21.18.34 1.5 1.6 31.10.2002 00.44.54 1.8 1.8 31.10.2002 06.51.40 1.9 1.5 31.10.2002 10.41.04 3.2 2.8 31.10.2002 11.22.12 2.4 2.2 31.10.2002 18.07.22 2.7 2.4 31.10.2002 18.50.10 2.1 1.8 31.10.2002 20.22.20 2.0 2.2 01.11.2002 01.29.51 2.5 2.2 01.11.2002 05.16.37 2.7 2.2 01.11.2002 15.32.03 3.1 2.9 02.11.2002 10.06.55 2.0 2.0 02.11.2002 17.09.54 2.8 2.3 02.11.2002 23.08.16 2.5 2.4 03.11.2002 00.22.30 2.3 2.1 03.11.2002 05.32.22 1.4 1.6 03.11.2002 05.35.14 2.1 1.8 03.11.2002 05.36.02 2.5 2.1 03.11.2002 10.21.59 3.5 3.4 03.11.2002 13.03.09 2.7 4.2 03.11.2002 13.43.40 2.2 2.0 04.11.2002 02.49.52 2.7 2.3 04.11.2002 05.29.55 1.9 1.7 04.11.2002 08.47.43 2.5 2.4 04.11.2002 10.52.35 3.0 2.7 04.11.2002 10.54.20 3.1 3.1 05.11.2002 18.54.47 2.7 2.4 05.11.2002 19.00.13 2.8 2.4 07.11.2002 09.03.18 2.3 1.9 07.11.2002 15.07.49 2.4 2.1 Appendix (continued). Time Origin MD ML Time Origin MD ML 227 Local magnitude estimate at Mt. Etna 07.11.2002 16.35.30 2.6 2.1 14.11.2002 03.31.10 2.8 2.6 16.11.2002 23.19.43 2.7 2.7 17.11.2002 09.26.21 2.8 2.8 17.11.2002 09.56.18 2.9 2.9 19.11.2002 10.42.03 2.6 2.5 24.11.2002 06.55.55 2.7 3.0 24.11.2002 07.38.29 2.8 2.5 24.11.2002 10.27.36 2.5 2.5 24.11.2002 11.03.36 3.0 2.9 24.11.2002 13.56.23 2.7 2.6 24.11.2002 14.53.02 2.8 3.0 24.11.2002 15.40.12 2.6 1.9 02.12.2002 12.20.38 2.8 2.9 03.12.2002 13.50.25 3.0 2.9 03.12.2002 21.07.00 2.8 3.2 05.12.2002 00.40.34 2.6 2.2 05.01.2003 15.38.56 2.1 1.7 20.01.2003 06.46.43 2.3 1.9 20.01.2003 21.26.50 1.9 2.0 21.01.2003 00.51.30 1.6 1.5 25.01.2003 03.29.18 2.7 2.5 25.01.2003 08.37.13 2.3 1.8 30.01.2003 20.25.06 1.5 0.6 01.02.2003 04.32.25 1.5 1.0 01.02.2003 09.20.03 2.1 1.2 01.02.2003 10.52.08 2.0 1.5 02.02.2003 02.32.51 1.4 1.1 02.02.2003 19.47.32 1.2 0.7 08.02.2003 19.37.09 2.0 0.8 09.02.2003 08.46.10 2.7 1.8 09.02.2003 13.26.52 2.2 1.0 10.02.2003 13.40.07 2.5 1.9 11.02.2003 00.43.44 2.5 1.8 12.02.2003 19.01.28 1.9 1.4 13.02.2003 05.29.10 2.9 2.4 13.02.2003 05.32.41 2.5 2.9 13.02.2003 05.33.01 3.8 3.8 13.02.2003 05.44.35 2.9 2.1 13.02.2003 05.48.00 2.5 1.2 13.02.2003 06.53.43 2.9 2.0 13.02.2003 16.15.32 1.7 0.5 13.02.2003 17.55.36 1.7 0.6 14.02.2003 04.44.11 2.6 1.8 14.02.2003 05.24.03 1.5 0.9 15.02.2003 19.11.33 1.5 0.7 16.02.2003 12.55.09 2.2 1.6 17.02.2003 01.30.43 2.5 1.9 18.02.2003 18.17.36 1.3 0.6 18.02.2003 22.15.06 2.6 1.9 18.02.2003 22.16.14 1.6 0.9 21.02.2003 13.46.23 2.0 0.9 21.02.2003 14.36.11 1.5 0.8 22.02.2003 01.08.39 2.0 1.0 23.02.2003 01.58.45 2.1 1.5 26.02.2003 18.35.02 2.1 1.6 01.03.2003 21.10.35 2.4 1.3 02.03.2003 11.55.07 1.4 1.1 03.03.2003 20.48.44 1.5 1.1 03.03.2003 20.49.23 1.4 0.7 03.03.2003 20.58.14 2.4 2.4 03.03.2003 21.02.48 2.6 2.0 04.03.2003 05.34.33 1.5 0.6 04.03.2003 05.38.06 1.5 0.6 05.03.2003 08.07.42 1.4 0.5 05.03.2003 08.09.53 2.2 1.6 08.03.2003 04.56.12 2.0 1.3 09.03.2003 07.55.59 3.0 3.0 09.03.2003 07.57.25 2.5 2.1 09.03.2003 08.00.05 2.3 1.9 09.03.2003 08.25.36 2.5 2.1 09.03.2003 08.28.48 2.5 2.3 09.03.2003 08.30.27 2.1 1.7 09.03.2003 08.31.31 2.2 1.6 09.03.2003 08.55.21 2.2 1.7 10.03.2003 05.04.53 2.5 1.6 11.03.2003 06.26.44 1.7 0.9 12.03.2003 01.44.39 1.2 1.5 14.03.2003 03.42.31 2.9 2.5 14.03.2003 22.19.26 1.8 1.8 Appendix (continued). Time Origin MD ML Time Origin MD ML 228 Salvatore D’Amico and Vincenza Maiolino 15.03.2003 00.14.57 1.2 1.0 16.03.2003 17.48.45 1.9 1.0 16.03.2003 21.58.06 2.0 1.3 17.03.2003 20.56.27 1.0 0.5 18.03.2003 01.49.19 1.5 0.9 18.03.2003 10.09.33 1.6 1.0 18.03.2003 18.14.12 2.1 1.7 19.03.2003 04.51.11 1.5 1.0 19.03.2003 15.42.51 2.1 1.6 20.03.2003 05.48.07 1.3 0.7 21.03.2003 15.29.59 1.7 1.1 22.03.2003 14.49.12 2.1 1.5 23.03.2003 04.02.03 1.5 1.1 23.03.2003 20.36.39 2.0 1.4 25.03.2003 03.57.14 2.6 1.7 25.03.2003 07.16.10 2.5 2.3 25.03.2003 08.12.00 2.3 2.1 25.03.2003 12.28.19 2.0 1.2 25.03.2003 13.12.53 2.1 1.6 25.03.2003 14.08.24 1.7 1.2 26.03.2003 08.25.48 2.0 1.3 26.03.2003 10.30.24 1.3 0.5 29.03.2003 14.40.29 1.5 0.9 29.03.2003 16.22.36 2.1 0.7 30.03.2003 13.42.30 1.3 0.8 30.03.2003 13.48.29 1.7 0.7 31.03.2003 12.49.13 2.5 1.9 01.04.2003 13.26.46 3.1 2.9 02.04.2003 17.15.31 1.8 0.9 05.04.2003 19.19.14 2.9 2.3 05.04.2003 19.45.27 2.1 1.3 05.04.2003 20.35.36 2.0 1.8 Appendix (continued). 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