Dr. Christos Evangelidis
Associate Researcher

// About



2000 - 2004

Ph.D. in Geophysics - Seismology
National Oceanography Centre, University of Southampton

Thesis: Three dimensional traveltime tomography of Ascension Island and the Mendocino Triple Junction area.
Supervisors: Prof. T.A. Minshull, Dr T.J. Henstock and Prof. R.B. Whitmarsh

1999 - 2000

M.Sc. Advanced Course in Geophysics
University of Durham
Dissertation: Time Lapse seismic surveying over long-wall mine workings
Supervisor: Prof. N.R. Goulty

1994 - 1999

Ptichion (B.Sc.) in Geology
University of Patra (Greece)



2016 - Present Associate Researcher in Seismology, Institute of Geodynamics, National Observatory of Athens.
2011 - 2015 Assistant Researcher in Seismology, Institute of Geodynamics, National Observatory of Athens.
2006 - 2010 Postdoctoral Researcher in Seismology, Institute of Geodynamics, National Observatory of Athens.
2004 Research Associate in Geophysics/Seismology, National Oceanography Centre, U.K.

// Publications

Papers (SCI Peer-Reviewed)

- E. Daskalakis, C.P. Evangelidis, J. Garnier, N.S. Melis, G. Papanicolaou and C. Tsogka, Robust seismic velocity change estimation using ambient noise recordings, Geophys.J.Int, doi: 10.1093/gji/ggw142, 2016

- K. Chousianitis, A. Ganas, C. P. Evangelidis, Strain and rotation rate patterns of mainland Greece from continuous GPS data and comparison between seismic and geodetic moment release, J. Geophys. Res., 120, doi:10.1002/2014JB011762, 2015

- C. P. Evangelidis, Imaging supershear rupture for the 2014 Mw 6.9 Northern Aegean earthquake by backprojection of strong motion waveforms, Geophys. Res. Lett., 42, doi:10.1002/2014GL062513, 2014

- C. P. Evangelidis and H. Kao, High-frequency source imaging of the October 23, 2011 Van (Eastern Turkey) earthquake by back-projection of strong motion waveforms, Geophys.J.Int, doi: 10.1093/gji/ggt437, 2013

- K. I. Konstantinou, C. P. Evangelidis, W.-T. Liang, N. S. Melis, I. Kalogeras, Seismicity, Vp/Vs and shear wave anisotropy variations during the 2011 unrest at Santorini caldera, southern Aegean, J. Volcanol. Geotherm. Res., 267, doi:http://dx.doi.org/10.1016/j.jvolgeores.2013.10.001, 2013.

- C. P. Evangelidis and N. S. Melis, Ambient Noise Levels in Greece as Recorded at the Hellenic Unified Seismic Network, Bull. seism. Soc. Am, , 102, no. 6, doi:10.1785/​0120110319, 2012.

- C. P. Evangelidis, W.-T. Liang, N. S. Melis, K. I. Konstantinou, Shear wave anisotropy beneath the Aegean inferred from SKS splitting observations, J. Geophys. Res., 116, B04314, doi:10.1029/2010JB007884, 2011.

- K. I. Konstantinou, C. P. Evangelidis, N. S. Melis, The 8 June 2008 Mw 6.4 Earthquake in Northwest Peloponnese, Western Greece: A Case of Fault Re-activation in an Overpressured Lower Crust?, Bull. seism. Soc. Am, 101, 1, doi:10.1785/0120100074, 2011.

- S. Rontogianni, K. I. Konstantinou, N. S. Melis, C. P. Evangelidis, Slab stress field in the Hellenic subduction zone as inferred from intermediate-depth earthquakes, Earth Plan. Sp., 63, 2, doi:10.5047/eps.2010.11.011, 2011.

- K. I. Konstantinou, N. S. Melis, S-J. Lee, C. P. Evangelidis, K. Boukouras, Rupture process and aftershocks relocation of the 8 June 2008 (Mw 6.4) earthquake in NW Peloponnese, Western Greece, Bull. seism. Soc. Am, 99, 3374-3389, doi:10.1785/0120080301, 2009.

- K. I. Konstantinou, S-J. Lee, C. P. Evangelidis, N. S. Melis, Source process and tectonic implications of the 8 January 2006 (Mw 6.7) Kythira earthquake, Southern Greece, Phys. Earth Planet. Int., 175, 3-4, doi:10.1016/j.pepi.2009.03.010, 2009.

- C. P. Evangelidis, K. I. Konstantinou, N. S. Melis, M. Charalambakis, G. N. Stavrakakis, Waveform Relocation and Focal Mechanism Analysis of an Eartquake Swarm in Trichonis Lake, Western Greece, Bull. seism. Soc. Am, 98, 2, 804-811, 2008.

- C. P. Evangelidis, T. A. Minshull, T. J. Henstock, Three-dimensional crustal structure of Ascension Island from active source seismic tomography, Geophys.J.Int, 159, 311-325, 2004.

Selected Published Abstracts

1. C. P. Evangelidis and H. Kao: Rupture plane identification of intermediate depth earthquakes in the Hellenic arc by back projection of local seismic waveforms, Geophysical Research Abstracts, Vol. 14, EGU2012-11610, 2012.

2. C. P. Evangelidis, N. S. Melis, I. Kalogeras: Monitoring broadband seismic noise in the Hellenic Unified Seismic Network (HUSN), Geophysical Research Abstracts, Vol. 13, 09022, 2011.

3. C. P. Evangelidis, N. S. Melis: Broadband seismic noise level analysis in Greece, 32nd General Assembly of the European Seismological Commission, 2010.

4. S. Mazza, N. Melis, M. Olivieri, C. Evangelidis, F. Mele, K. Boukouras, L. Scognamiglio, G. Stavrakakis: Toward a Joint INGV-NOA Earthquake Location Schema for the Ionian Sea, 31st General Assembly of the European Seismological Commission, 2008.

5. C. P. Evangelidis, N. S. Melis, K. I. Konstantinou, W-T. Liang: SKS splitting measurements and shear wave anisotropy in the upper mantle beneath the Aegean, Geophysical Research Abstracts, Vol. 10, 07755, 2008.

6. K. I. Konstantinou, S-J. Lee, C. P. Evangelidis, N. S. Melis: Finite Fault Inversion of the January 8 2006 (Mw 6.7) Kythira Earthquake, Southern Greece, Geophysical Research Abstracts, Vol. 10, 08498, 2008.

7. H. Zhang, C. Thurber, T. Brocher, Y. Liu, C. Evangelidis: A new regional seismic tomography model for Northern California, Seismological Research Letters, 77, 271, SSA Annual Meeting, 2006.

8. C. P. Evangelidis, T. J. Henstock: Three-dimensional velocity structure at the Mendocino Triple Junction area from traveltime tomography and earthquake re-location, Geophysical Research Abstracts, Vol. 7, 07199, European Geosciences Union, 2005.

9. C. P. Evangelidis, T. J. Henstock: Three-dimensional crustal structure at the Mendocino Triple Junction from a combination of active source seismic tomography methods, Geophysical Research Abstracts, Vol. 6, 01052, European Geophysical Society, 2004.

10. C. P. Evangelidis, P. M. Shearer, T. J. Henstock: Earthquake relative relocation near the Mendocino Triple Juction, Eos Trans. AGU, 84(46),Fall Meet. Suppl., Abstract S21D-0327, 2003.

11. T. A. Minshull, N.C. Mitchell, O. Ishizuka, C. P. Evangelidis: Vertical Motions and Lithosphere Rheology at Ascension Island, Eos Trans. AGU, 84(46),Fall Meet. Suppl., Abstract V11B-06, 2003.

12. C. P. Evangelidis, P. M. Shearer: Improving earthquake relative location near the Mendocino Triple Junction, northern California, ECS 1st International Workshop on Earthquake Prediction, Athens, November 2003.

13. C. P. Evangelidis, T. J. Henstock, T. A. Minshull: Three-dimensional crustal structure at the Mendocino Triple Junction from active source seismic tomography, Geophysical Research Abstracts, Vol. 5, 11860, European Geophysical Society, 2003.

14. C. P. Evangelidis, T. A. Minshull, T. J. Henstock: Three-dimensional crustal structure of Ascension Island from active source seismic tomography, European Geophysical Society General Assembly 2003.

// Research

Seismic Tomography

The accomplished research, as part of my Ph.D., includes the use of two active source wide angle datasets from contrasting geological regions, Ascension Island in equatorial S. Atlantic and Mendocino Triple Junction. Traveltime regularized tomography of refracted and reflected phases was performed to obtain the 3D velocity structures. Crustal velocities and the Moho depth of the Ascension volcanic edifice were revealed using one of the most densely sampled 3D wide-angle datasets for volcanic islands currently available. Traveltimes of first and second arrivals were inverted by seeking a layer-interface minimum structure model. The resulting velocity structure was tested by gravity modeling and compared with other volcanic islands and seamounts (see Evangelidis et. al., 2004 in GJI). The second and largest dataset comes from the Mendocino Triple Junction 1993-94 PASSCAL wide-angle 3D experiment. The experiment spans a change in tectonics from the southern end of the Cascadia subduction zone into the northernmost part of the San Andreas strike-slip fault system and covers an area of 280x270 km. A velocity model derived from first arrival times (Pg and Pn) is complemented by results derived from the first crustal arrivals (Pg) alone, which improves constraints on the lower crustal structure. Checkerboard tests showed that the final velocity models resolve features with 20 km lateral extent at depths up to 15 km and with 30 km lateral extent to the base of the crust. Distinct velocity structures were determined for the main tectonic elements, with some local variability (see abstracts: Evangelidis et. al, 2003, Evangelidis and Henstock, 2005 and Zhang et. al. 2006).

Earthquake Relocation - Waveform CrossCorrelation

As part of a scientific visit in IGPP, San Diego, I relocated ~30000 earthquakes recorded between 1977 and 2002 near the Mendocino Triple Junction. Although absolute earthquake locations will depend on the 3D velocity structure, relative event locations within seismicity clusters can be accurately improved through the use of source-specific station terms and waveform cross-correlation, using 1D velocity models extracted from a smooth 3D wide-angle model (see abstract: Evangelidis and Shearer, 2003). I used the same relocation method to study several aftershock sequences in Greece adapting them for a sparser and smaller recording seismic network. At first, the method was successfully applied to an earthquake swarm in Western Greece (see Evangelidis et. al., 2008 in BSSA). This was the first study in Greece applying waveform cross-correlation methods. Then it was applied to the moderate Kythira earthquake (6.7 Mw), where most relocated aftershocks reveal a tight cluster around the mainshock at depths between 44 and 53 km (see Konstantinou et. al., 2009). The following study of the moderate NW Peloponnese earthquake (6.4 Mw) revealed three distinct aftershock clusters at depths 15-25 km (see Konstantinou et. al. , 2009 in BSSA). Recently, using data from January 2011 until June 2012 recorded in local seimic network in Santorini Island I calculated accurate relative locations for 490 events utilizing both catalog and waveform cross-correlation differential travel times of P- and S-phases. The distribution of relocated events exhibits a large cluster between Thera and Nea Kameni islands along the caldera rim, suggesting the activation of preexisting ring fault (see Kostantinou et. al., 2013 in J. Volcanol. Geotherm. Res.).

Seismic Anisotropy

SKS wave splitting is the most useful tool to investigate upper mantle anisotropy. We analyzed these teleseismic phases recorded at the dense EGELADOS network in south Aegean and the backbone seismic networks that permanently operate in Greece (see Evangelidis et. al., 2011). We especially focused on the backarc and the near trench areas where the density of our measurements was the largest. We interpreted this shear wave splitting data set, integrating all available information for the Aegean region, which includes GPS velocities, the current strain field, metamorphic core complexes stretching lineations, the 3D velocity structure from tomography studies and lithospheric boundaries derived from receiver functions. In general, fast anisotropy directions are trench perpendicular in the back‐arc area and trench parallel near the trench with anisotropy measurements near the volcanic arc marking the transition between these two regions. Our preferred source of anisotropy in the back‐arc region is the mantle wedge flow, induced by the retreating descending slab. The westernmost termination of the trench reveals directions parallel with the Kefalonia Transform Fault and perpendicular to the convergence boundary. Beneath Peloponnese, the trench‐parallel flow is probably located beneath the shallow dipping slab. In western Crete the anisotropy pattern changes to trench perpendicular, with a possible subslab source. Good nulls in central east Crete indicate a change in the anisotropy origin toward the east. At the easternmost side of the trench, fast directions are trench parallel. This reflects a similar subslab flow that may become toroidal around the slab edge beneath western Turkey.

Ambient Seismic Noise

A daily noise analysis in a routine procedure is needed by network operators to monitor network performance, in terms of overall station quality and the level of noise at each site. The characteristics of ambient noise across Greece as recorded at the Hellenic Unified Seismic Network (HUSN) were investigated (see Evangelidis and Melis, 2012 in BSSA). Power spectral densities (PSDs) and their corresponding probability density functions (PDFs) have been estimated for ~110 broadband seismic stations using the continuous waveform data for a 4-yr period, 2007 to 2010 inclusive. At high frequencies (> 7 Hz), the main source of noise is cultural with strong diurnal variations. Stations with constantly increased noise levels across this band, indicate poor vault construction or site selection and provide an indication to the network operators for possible structural improvements or even station relocations. The microseismic noise levels show a clear seasonal variation at all stations. Specifically, for the double frequency (period range 4-8 sec) band, the noise peak is observed at all HUSN stations and it is correlated well with local sea wave height measurements at buoys deployed in the Aegean and the Ionian seas. This indicates that HUSN seismic network also monitors local sea weather conditions within a few hundred kilometers range. The longer period single frequency band is affected by sea/weather conditions at much longer distances in the North Atlantic. The HUSN mode noise model (HMLNM) that represents the highest probability ambient noise level in Greece was also calculated. This model is a realistic noise threshold for future seismic station installations and studies that make use of seismic noise. Currently, I study the recorded noise in the strong motion network trying to evaluate station performance and their potential use in the 24/7 analysis for earthquake parameters estimation (see abstract: Evangelidis et. al, 2011).

Non-Volcanic Tremor

Since March 2010, I scan daily the HUSN continuous waveform data trying to identify any potential non-volcanic tremor in the Hellenic trench. I use the Tremor Activity Monitoring System (TAMS ) by Kao et. al.(2007, doi:10.1029/2007GL030822). The algorithm is parametrized for the specifications of the HUSN network. Until now, there are no independently identified tremor episodes in Greece that could help in the optimization and fine tuning of the method. I recently applied the same method for volcanic tremor modeling in the Santorini volcano that is currently under volcanic unrest.

Earthquake Backprojection

Earthquake backprojection methods are the new alternative tool to identify the spatiotemporal distribution of seismic sources. We apply the Source-Scanning Algorithm (SSA), an earthquake backprojection approach, to identify the rupture plane and possible source time function asperities of intermediate depth earthquakes in the Hellenic arc (see abstract Evangelidis and Kao, 2012) . We use P-waveform envelopes from recordings on local broadband stations at epicentral distances as much as 200~km. At each grid point of a predefined source volume we sum the normalized observed amplitudes at the corresponding predicted arrival times for each station with an appropriate time correction. The produced composite brightness image in both space and time resembles the earthquake rupture plane, and the source asperities. Intermediate depth earthquakes are the ideal candidates for this type of analysis, since the P-wave train is well defined and separated from secondary phases. Moreover, the small number of aftershocks can not define with certainty the true rupture plane, that constrain the predominant stress field and the mechanisms that produces them. We apply the method to two strike slip moderate (Mw 6.1-6.5) intermediate depth earthquakes at the southeastern Hellenic arc that have not been studied before in order to image the true fault planes. Initial results showed that the Mw 6.1 Kasos event on 01/04/2011 ruptured at the NW-SE plane whereas the Mw 6.4 Rhodes event on 15/07/2008 ruptured at the NNW-SSE plane. This indicates a similar stress field and intermediate depth mechanism.