A precise understanding of crustal structure is essential to the fields of geodynamics, seismology and certain branches of geophysics. A boundary between the crust and the mantle is known as the Mohorovičić discontinuity, simply referred to as the ‘Moho’. Moho geometry and depth have been extensively studied in Europe, but there are still regions with little information about it. One such area is the northern Baltics, Latvia in particular. So far, only one seismic refraction profile, spanning from Sovetsk (Kaliningrad) to Kohtla-Järve (Estonia), has been used to study the deep structure of the Earth in Latvia. We propose gravity inversion (Parker–Oldenburg algorithm) to gain more insight into the Moho depth of Latvia. Multiple gravity sources are combined in a single data set with the regression-kriging method. Gravity data are then iteratively filtered with various wavelength low-pass filters. We use different combinations of these filtered datasets and varying input parameters – mean depth to the Moho and density contrast between the crust and the mantle – to carry out multiple iterations of the inversion, validating the results by seismic refraction profiles available for Latvia. The calculated Moho depth varies from 41.5 km in the southern and northeastern parts of Latvia to 46.5 km in the northern part of Latvia and the Gulf of Riga. We conclude that gravity inversion with the Parker–Oldenburg algorithm can be used as an alternative to the seismic exploration of the Moho, especially in places where there is a shortage of earlier seismic data. The obtained results also show that it is necessary to create multiple models with various combinations of input values when using the Parker–Oldenburg inversion algorithm.
Agnew, D. C. 2002. History of seismology. In International Handbook of Earthquake and Engineering Seismology, Part A (Lee, W. H., ed.), pp. 3–11. Academic Press, San Diego.
https://doi.org/10.1016/S0074-6142(02)80203-0
Ankudinov, S., Sadov, A. & Brio, H. 1994. Crustal structure of Baltic countries on the basis of deep seismic sounding data. Proceedings of the Estonian Academy of Sciences, Geology, 43, 129–136 [in Russian, with English summary].
Artemieva, I. M. & Thybo, H. 2013. EUNAseis: A seismic model for Moho and crustal structure in Europe, Greenland, and the North Atlantic region. Tectonophysics, 609, 97–153.
https://doi.org/10.1016/j.tecto.2013.08.004
Bagherbandi, M. 2012. A comparison of three gravity inversion methods for crustal thickness modelling in Tibet plateau. Journal of Asian Earth Sciences, 43, 89–97.
https://doi.org/10.1016/j.jseaes.2011.08.013
Bogatikov, O. A. & Birkis, A. P. 1973. Magmatizm dokembriya Zapadnoj Latvii [Magmatism of the Precambrian of Western Latvia]. Nauka, Moscow, 138 pp. [in Russian].
Bogdanova, S., Gorbatschev, R., Grad, M., Janik, T., Guterch, A., Kozlovskaya, E., Motuza, G., Skridlaite, G., Starostenko, V., Taran, L. & EUROBRIDGE and POLONAISE working groups. 2006. EUROBRIDGE: new insight into the geodynamic evolution of the East European Craton. Geological Society, London, Memoirs, 32, 599–625.
https://doi.org/10.1144/GSL.MEM.2006.032.01.36
Bogdanova, S. V., Bingen, B., Gorbatschev, R., Kheraskova, T. N., Kozlov, V. I., Puchkov, V. N. & Volozh, Yu. A. 2008. The East European Craton (Baltica) before and during the assembly of Rodinia. Precambrian Research, 160, 23–45.
https://doi.org/10.1016/j.precamres.2007.04.024
Bogdanova, S., Gorbatschev, R., Skridlaite, G., Soesoo, A., Taran, L. & Kurlovich, D. 2015. Trans-Baltic Palaeoproterozoic correlations towards the reconstruction of supercontinent Columbia/Nuna. Precambrian Research, 259, 5–53.
https://doi.org/10.1016/j.precamres.2014.11.023
Braitenberg, C., Zadro, M., Fang, J., Wang, Y. & Hsu, H. T. 2000. The gravity and isostatic Moho undulations in Qinghai-Tibet plateau. Journal of Geodynamics, 30, 489–505.
https://doi.org/10.1016/S0264-3707(00)00004-1
Brangulis, A. J. & Kaņevs, S. 2002. Latvijas tektonika [Tectonics of Latvia]. Latvian State Geological Survey, Riga, 50 pp. [in Latvian].
Brangulis, A. J., Kuršs, V., Misāns, J. & Stinkulis, Ģ. 1998. Latvijas ģeoloģija [Geology of Latvia]. Latvian State Geological Survey, Riga, 70 pp. [in Latvian].
Brio, H. S. & Shtehman, I. P. 1967. Otchet o kompleksnoj geologogidrogeologicheskoj i inzhenerno-geologicheskoj s´´emke mashtaba 1:200 000 na territorii lista О-35-ХIХ. [Report on Integrated Geological-Hydrogeological and Engineering Geological Survey of the Scale 1:200 000 in the Territory of Map Sheet O-35-XIX]. USSR Ministry of Geology [in Russian].
Cocks, L. R. M. & Torsvik, T. H. 2005. Baltica from the late Precambrian to mid-Palaeozoic times: The gain and loss of a terrane’s identity. Earth-Science Reviews, 72, 39–66.
https://doi.org/10.1016/j.earscirev.2005.04.001
Corchete, V., Chourak, M. & Khattach, D. 2010. A methodology for filtering and inversion of gravity data: an example of application to the determination of the Moho undulation in Morocco. Engineering, 2, 149–159.
https://doi.org/10.4236/eng.2010.23021
Dziewonski, A. M. & Anderson, A. L. 1981. Prelimenary reference Earth model. Physics of the Earth and Planetary Interiors, 25, 297–356.
https://doi.org/10.1016/0031-9201(81)90046-7
Förste, C., Bruinsma, S., Rudenko, S., Abrikosov, O., Lemoine, J. M., Marty, J. C., Neumayer, K. H. & Biancale, R. 2016. EIGEN-6S4 A Time-Variable Satellite-Only Gravity Field Model to d/o 300 Based on LAGEOS, GRACE and GOCE Data from the Collaboration of GFZ Potsdam and GRGS Toulouse. European Geosciences Union, General Assembly 2015. Vienna, Austria, 26 pp.
Gibbard, P. L. & Lewin, J. 2016. André Dumont medallist lecture 2014: Filling the North Sea Basin: Cenozoic sediment sources and river styles. Geologica Belgica, 19, 201–217.
https://doi.org/10.20341/gb.2015.017
Gómez-Ortiz, D. & Agarwal, B. N. P. 2005. 3DINVER.M: A MATLAB program to invert the gravity anomaly over a 3D horizontal density interface by Parker–Oldenburg’s algorithm. Computers & Geosciences, 31, 513–520.
https://doi.org/10.1016/j.cageo.2004.11.004
Gómez-Ortiz, D., Tejero-López, R., Babín-Vich, R. & Rivas-Ponce, A. 2005. Crustal density structure in the Spanish central system derived from gravity data analysis (central Spain). Tectonophysics, 403, 131–149.
https://doi.org/10.1016/j.tecto.2005.04.006
Grad, M., Janik, T., Guterch, A., Środa, P., Czuba, W., Astapenko, V. N., … Smirnov, A. 2006. Lithospheric structure of the western part of the East European Craton investigated by deep seismic profiles. Geological Quarterly, 50, 9–22.
Grad, M., Tiira, T., Behm, M., Belinsky, A. A., Booth, D. C., Brückl, E. … Zolotov, E. E. 2009. The Moho depth map of the European Plate. Geophysical Journal International. 176, 279–292.
https://doi.org/10.1111/j.1365-246X.2008.03919.x
Gräler, B., Pebesma, E. & Heuvelink, G. 2016. Spatio-temporal interpolation using gstat. The R Journal, 8, 204–218.
https://doi.org/10.32614/RJ-2016-014
Hengl, T. 2006. Finding the right pixel size. Computers & Geosciences, 32, 1283–1298.
https://doi.org/10.1016/j.cageo.2005.11.008
Hengl, T. 2009. A Practical Guide to Geostatistical Mapping. EN Scientific and Technical Research series, Office for official Publications of the European Communities, Luxembourg, 293 pp.
Hengl, T., Heuvelink, G. & Stein, A. 2003. Comparison of Kriging with External Drift and Regression-Kriging. Technical Note, ITC 17, 17 pp.
Hengl, T., Heuvelink, G. B. M. & Rossiter, D. G. 2007. About regression-kriging: From equations to case studies. Computers & Geosciences, 33, 1301–1315.
https://doi.org/10.1016/j.cageo.2007.05.001
Hrvoje, T. 2017. The Earth’s Inner Core Revealed by Observational Seismology. Cambridge University Press, 234 pp.
Jensen, S. L., Thybo, H. & The POLONAISE’97 Working group. 2002. Moho topography and lower crustal wide-angle reflectivity around the TESZ in southern Scandinavia and northeastern Europe. Tectonophysics, 360, 187–213.
https://doi.org/10.1016/S0040-1951(02)00354-2
Kaminskis, J. 2010. Latvijas Ģeoīda modelis un tā attīstība: promocijas darbs [The Geoid Model of Latvia and Its Evolution]. PhD Thesis, Faculty of Civil Engineering, Riga Technical University [in Latvian].
Kennett, B. L. N. & Engdahl, E. R. 1991. Travel times for global earthquake location and phase association. Geophysical Journal International, 105, 429–465.
https://doi.org/10.1111/j.1365-246X.1991.tb06724.x
Kennett, B. L. N., Engdahl, E. R. & Buland, R. 1995. Constraints on seismic velocities in the Earth from traveltimes, Geophysical Journal International, 122, 108–124.
https://doi.org/10.1111/j.1365-246X.1995.tb03540.x
Kozlovskaya, E., Karatayev, G. I. & Yliniemi, J. 2001. Lithosphere structure along the northern part of EUROBRIDGE in Lithuania: results from integrated interpretation of DSS and gravity data. Tectonophysics, 339, 177–191.
https://doi.org/10.1016/S0040-1951(01)00038-5
Kozlovskaya, E., Taran, L. N. & Yliniemi, J. 2002. Deep structure of the crust along the Fennoscandia–Sarmatia Junction Zone (central Belarus): results of a geophysical–geological integration. Tectonophysics, 358, 97–120.
https://doi.org/10.1016/S0040-1951(02)00419-5
Lefort, J. P. & Agarwal, B. N. P. 2000. Gravity and geomorphological evidence for a large crustal bulge cutting across Brittany (France): a tectonic response to the closure of the Bay of Biscay. Tectonophysics, 323, 149–162.
https://doi.org/10.1016/S0040-1951(00)00103-7
Li, Z. X., Bogdanova, S. V., Collins, A. S., Davidson, A., De Waele, B., Ernst, R. E., Fitzsimons, I. C. W., Fuck, R. A., Gladkochub, D. P., Jacobs, J., Karlstrom, K. E., Lu, S., Natapov, L. M., Pease, V., Pisarevsky, S. A., Thrane, K. & Vernikovsky, V. 2008. Assembly, configuration, and break-up history of Rodinia: a synthesis. Precambrian Research, 160, 179–210.
https://doi.org/10.1016/j.precamres.2007.04.021
Mohorovičić, A. 1910. Potres of 8.X.1909. Godišnje izvješće zagrebačkog meteorološkog observatorija, 9(4/1), 1–56 [in Croatian] [English translation in 1992: Earthquake of 8 October 1909. Geofizika, 9, 3–55].
Molinari, I. & Morelli, A. 2011. EPcrust: a reference crustal model for the European Plate. Geophysical Journal International, 185, 352–364.
https://doi.org/10.1111/j.1365-246X.2011.04940.x
Mondal, A., Khare, D., Kundu, S., Mondal, S., Mukherjee, S. & Mukhopadhyay, A. 2017. Spatial soil organic carbon (SOC) prediction by regression kriging using remote sensing data. The Egyptian Journal of Remote Sensing and Space Science, 20, 61–70.
https://doi.org/10.1016/j.ejrs.2016.06.004
Morelli, A. & Dziewonski, A. M. 1993. Body-wave traveltimes and a spherically symmetric P- and S-wave velocity model. Geophysical Journal International, 112, 178–194.
https://doi.org/10.1111/j.1365-246X.1993.tb01448.x
Nance, R. D., Murphy, J. B. & Santosh, M. 2014. The supercontinent cycle: A retrospective essay. Gondwana Research, 25, 4–29.
https://doi.org/10.1016/j.gr.2012.12.026
Oldenburg, D. W. 1974. The inversion and interpretation of gravity anomalies. Geophysics, 39, 526–536.
https://doi.org/10.1190/1.1440444
Ostrovsky, A. A, Flueh, E. R. & Luosto, U. 1994. Deep seismic structure of the Earth’s crust along the Baltic Sea profile. Tectonophysics, 233, 279–292.
https://doi.org/10.1016/0040-1951(94)90246-1
Parker, R. L. 1973. The rapid calculation of potential anomalies. Geophysical Journal of the Royal Astronomical Society, 31, 447–455.
https://doi.org/10.1111/j.1365-246X.1973.tb06513.x
Prasanna, H. M. I., Chen, W. & Iz, H. B. 2013. High resolution local Moho determination using inversion: A case study in Sri Lanka. Journal of Asian Earth Sciences, 74, 62–70.
https://doi.org/10.1016/j.jseaes.2013.06.005
Prodehl, C., Kennett, B., Artemieva, I. M. & Thybo, H. 2013. 100 years of seismic research on the Moho. Tectonophysics, 609, 9–44.
https://doi.org/10.1016/j.tecto.2013.05.036
Python Software Foundation. 2019. Python Language Reference, version 2.7.14. Available at
http://www.python.org
R Core Team. 2019. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria. URL http://www.R-project.org/.
Sadov, A. & Penzina, V. 1986. Otchet: Izuchenie glubinnogo stroeniya zemnoj kory (regional´nye sejsmorazvedochnye raboty GSZ) po geotraversu Sovetsk–Riga–Kohtla-Yarve [Report: Study of the Deep Structure of the Earth’s Crust (Regional Seismic Exploration Works by GSZ) on the geoprofile Sovetsk–Riga–Kohtla-Järve]. USSR Ministry of Geology, Kaliningrad [in Russian].
Scotese, C. R. 2001. Atlas of Earth History, Volume 1, Paleogeography. PALEOMAP Project, 52 pp.
Shearer, P. M. 2009. Introduction to Seismology. Second edition, Cambridge University Press, 234 pp.
Tesauro, M., Kaban, M. K. & Cloetingh, S. A. P. L. 2008. EuCRUST-07: a new reference model for the European crust. Geophysical Research Letters, 35, L05313.
https://doi.org/10.1029/2007GL032244
Torsvik, T. H. & Cocks, L. R. M. 2005. Norway in space and time: A Centennial cavalcade. Norwegian Journal of Geology, 85, 73–86.
Tuuling, I. 2019. The Leba Ridge–Riga–Pskov Fault Zone – a major East European Craton interior dislocation zone and its role in the early Palaeozoic development of the platform cover. Estonian Journal of Earth Sciences, 68, 161–189.
https://doi.org/10.3176/earth.2019.12
Wu, Q., Merchant, F. & Castleman, K. R. 2008. Microscope Image Processing. First edition. Elsevier, Burlington, San Diego, London, 576 pp.
Yliniemi, J., Tiira, T., Luosto, U., Komminaho, K., Giese, R., Motuza, G., Nasedkin, V., Jacyna, J., Seckus, R., Grad, M., Czuba, W., Janik, T., Guterch, A. & Lund, C. E. 2001. EUROBRIDGE’95: Deep seismic profiling within the East European Craton. Tectonophysics, 339, 153–175.
https://doi.org/10.1016/S0040-1951(01)00037-3
Zandersons, V., Ješkins, J., Karušs, J., Liepiņš, I. & Sproģis, V. 2018. First rock density model of Latvian crystalline basement. Geophysical Research Abstracts. EGU General Assembly 2018, 20, 2 pp.
Zhang, Y., Ji, W., Saurette, D. D., Easher, T. H., Li, H., Shi, Z., Adamchuk, V. I. & Biswas, A. 2020. Three-dimensional digital soil mapping of multiple soil properties at a field-scale using regression kriging. Geoderma, 366, 114253.
https://doi.org/10.1016/j.geoderma.2020.114253
