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Publications (10 of 36) Show all publications
DeFelipe, I., Alcalde, J., Ivandic, M., Marti, D., Ruiz, M., Marzan, I., . . . Carbonell, R. (2021). Reassessing the lithosphere: SeisDARE, an open-access seismic data repository. Earth System Science Data, 13(3), 1053-1071
Open this publication in new window or tab >>Reassessing the lithosphere: SeisDARE, an open-access seismic data repository
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2021 (English)In: Earth System Science Data, ISSN 1866-3508, E-ISSN 1866-3516, Vol. 13, no 3, p. 1053-1071Article in journal (Refereed) Published
Abstract [en]

Seismic reflection data (normal incidence and wide angle) are unique assets for solid Earth sciences as they provide critical information about the physical properties and structure of the lithosphere as well as about the shallow subsurface for exploration purposes. The resolution of these seismic data is highly appreciated; however they are logistically complex and expensive to acquire, and their geographical coverage is limited. Therefore, it is essential to make the most of the data that have already been acquired. The collation and dissemination of seismic open-access data are then key to promote accurate and innovative research and to enhance new interpretations of legacy data. This work presents the Seismic DAta REpository (SeisDARE), which is, to our knowledge, one of the first comprehensive open-access online databases that stores seismic data registered with a permanent identifier (DOI). The datasets included here are openly accessible online and guarantee the FAIR (findable, accessible, interoperable, reusable) principles of data management, granting the inclusion of each dataset in a statistics referencing database so its impact can be measured. SeisDARE includes seismic data acquired in the last 4 decades in the Iberian Peninsula and Morocco. These areas have attracted the attention of international researchers in the fields of geology and geophysics due to the exceptional outcrops of the Variscan and Alpine orogens and wide foreland basins, the crustal structure of the offshore margins that resulted from a complex plate kinematic evolution, and the vast quantities of natural resources contained within. This database has been built thanks to a network of national and international institutions, promoting a multidisciplinary research and is open for international data exchange and collaborations. As part of this international collaboration, and as a model for inclusion of other global seismic datasets, SeisDARE also hosts seismic data acquired in Hardeman County, Texas (USA), within the COCORP project (Consortium for Continental Reflection Profiling). SeisDARE aims to make easily accessible old and recently acquired seismic data and to establish a framework for future seismic data management plans. SeisDARE is freely available at https://digital.csic.es/handle/10261/101879 (a detailed list of the datasets can be found in Table 1), bringing endless research and teaching opportunities to the scientific, industrial, and educational communities.

Place, publisher, year, edition, pages
Copernicus PublicationsCOPERNICUS GESELLSCHAFT MBH, 2021
Keywords
OCEAN-CONTINENT TRANSITION; NORTH-IBERIAN MARGIN; CRUSTAL STRUCTURE; CANTABRIAN MOUNTAINS; SW-IBERIA; LATERAL VARIATIONS; WESTERN PYRENEES; ATLAS MOUNTAINS; DEEP BASEMENT; VARISCAN BELT
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-441870 (URN)10.5194/essd-13-1053-2021 (DOI)000630176700002 ()
Available from: 2021-05-06 Created: 2021-05-06 Last updated: 2024-01-15Bibliographically approved
Amini, S., Roberts, R. & Lund, B. (2020). Directivity analysis of the 2017 December Kerman earthquakes in Eastern Iran. Journal of Seismology, 24, 531-547
Open this publication in new window or tab >>Directivity analysis of the 2017 December Kerman earthquakes in Eastern Iran
2020 (English)In: Journal of Seismology, ISSN 1383-4649, E-ISSN 1573-157X, Vol. 24, p. 531-547Article in journal (Refereed) Published
Abstract [en]

Using an empirical Green’s function (EGF) approach and data from local to regional distances we analyzed rupture propagation directivity in the three mainshocks (ML 6.0–6.1) and in six of the largest aftershocks (ML 5.0 – 5.5) of the 2017 Kerman, Iran, seismic sequence. The EGF procedure was based on data from smaller events (ML 4.0 – 4.8). Deconvolution was applied separately to P and S phases. Using the P-wave data, we calculated relative source-time functions and examined azimuthal variations in rupture duration. In the S-wave analysis, we investigated along strike rupture directivity of the mainshocks and the largest aftershocks by evaluating azimuthal variation of the amplitude spectra. Two of the mainshocks and four of the aftershocks clearly showed rupture propagation from the south-east toward the north-west. The third mainshock and one of the aftershocks suggested almost bilateral rupture propagation, and one aftershock showed rupture directivity to the southeast. It seems that the rupture propagation direction in the area is generally to the north-west and the events which have different propagation directions are located within the NW and SE ends of the faulting area. We suggest that the general rupture propagation direction in the area is steered by regional tectonic stress field regarding the faulting orientations which have been affected by stress redistribution around a restraining bend.

Place, publisher, year, edition, pages
Springer, 2020
Keywords
triplet earthquake, directivity, Empirical Green's function, spectral deconvolution, restraining bend, Eastern Iran
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-407245 (URN)10.1007/s10950-020-09913-8 (DOI)000530268700001 ()
Available from: 2020-03-21 Created: 2020-03-21 Last updated: 2024-02-28Bibliographically approved
Wagner, F., Tryggvason, A., Roberts, R. & Gudmundsson, Ó. (2019). Processing automatic seismic event detections: an iterative sorting algorithm improving earthquake hypocentres using interevent cross-correlation. Geophysical Journal International, 219(2), 1268-1280
Open this publication in new window or tab >>Processing automatic seismic event detections: an iterative sorting algorithm improving earthquake hypocentres using interevent cross-correlation
2019 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 219, no 2, p. 1268-1280Article in journal (Refereed) Published
Abstract [en]

We present an iterative classification scheme using interevent cross-correlation to update an existing earthquake catalogue with similar events from a list of automatic seismic event detections. The algorithm automatically produces catalogue quality events, with improved hypocentres and reliable P- and S-arrival time information. Detected events are classified into four event categories with the purpose of using the top category, with the highest assessed event quality and highest true-to-false ratio, directly for local earthquake tomography without additional manual analysis. The remaining categories have varying proportions of lower quality events, quality being defined primarily by the number of observed phase onsets, and can be viewed as different priority groups for manual inspection to reduce the time spent by a seismic analyst. A list of 3348 event detections from the geothermally active volcanic region around Hengill, southwest Iceland, produced by our migration and stack detector (Wagner et al. 2017), was processed using a reference catalogue of 1108 manually picked events from the same area. P- and S-phase onset times were automatically determined for the detected events using correlation time lags with respect to manually picked phase arrivals from different multiple reference events at the same station. A significant improvement of the initial hypocentre estimates was achieved after relocating the detected events using the computed phase onset times. The differential time data set resulting from the correlation was successfully used for a double-difference relocation of the final updated catalogue. The routine can potentially be implemented in real-time seismic monitoring environments in combination with a variety of seismic event/phase detectors.

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-376655 (URN)10.1093/gji/ggz362 (DOI)000491050200039 ()
Funder
Swedish Research Council, 2008:3754
Available from: 2019-02-07 Created: 2019-02-07 Last updated: 2020-01-03Bibliographically approved
Amini, S., Roberts, R., Raeesi, M., Shomali, Z. H., Lund, B. & Zarifi, Z. (2018). Fault slip and identification of the second fault plane in the Varzeghan earthquake doublet. Journal of Seismology, 22(4), 815-831
Open this publication in new window or tab >>Fault slip and identification of the second fault plane in the Varzeghan earthquake doublet
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2018 (English)In: Journal of Seismology, ISSN 1383-4649, E-ISSN 1573-157X, Vol. 22, no 4, p. 815-831Article in journal (Refereed) Published
Abstract [en]

An intraplate earthquake doublet, with 11-min delay between the events, devastated the city of Varzeghan in northwestern Iran on August 11, 2012. The first Mw 6.5 strike-slip earthquake, which occurred after more than 200 years of low seismicity, was followed by an Mw 6.4 oblique thrust event at an epicentral separation of about 6 km. While the first event can be associated with a distinct surface rupture, the absence of a surface fault trace and no clear aftershock signature makes it challenging to identify the fault plane of the second event. We use teleseismic body wave inversion to deduce the slip distribution in the first event. Using both P and SH waves stabilize the inversion and we further constrain the result with the surface rupture extent and the aftershock distribution. The obtained slip pattern shows two distinct slip patches with dissimilar slip directions where aftershocks avoid high-slip areas. Using the estimated slip for the first event, we calculate the induced Coulomb stress change on the nodal planes of the second event and find a preference for higher Coulomb stress on the N-S nodal plane. Assuming a simple slip model for the second event, we estimate the combined Coulomb stress changes from the two events on the focal planes of the largest aftershocks. We find that 90% of the aftershocks show increased Coulomb stress on one of their nodal planes when the N-S plane of the second event is assumed to be the correct fault plane.

Place, publisher, year, edition, pages
SPRINGER, 2018
Keywords
Earthquake source estimation, Teleseismic body waves, Slip inversion, Coulomb stress changes, Asia
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-359999 (URN)10.1007/s10950-018-9734-0 (DOI)000436110300001 ()
Available from: 2018-09-14 Created: 2018-09-14 Last updated: 2020-03-21Bibliographically approved
Leptokaropoulos, K., Adamaki, A., Roberts, R., Gkarlaouni, C. & Paradisopoulou, P. (2018). Impact of Magnitude Uncertainties on Seismic Catalogue Properties. Geophysical Journal International, 213(2), 940-951
Open this publication in new window or tab >>Impact of Magnitude Uncertainties on Seismic Catalogue Properties
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2018 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 213, no 2, p. 940-951Article in journal (Refereed) Published
Abstract [en]

Catalogue-based studies are of central importance in seismological research, to investigate the temporal, spatial and size distribution of earthquakes in specified study areas. Methods for estimating the fundamental catalogue parameters like the Gutenberg–Richter (G-R) b-value and the completeness magnitude (Mc) are well established and routinely applied. However, the magnitudes reported in seismicity catalogues contain measurement uncertainties which may significantly distort the estimation of the derived parameters. In this study, we use numerical simulations of synthetic data sets to assess the reliability of different methods for determining b-value and Mc, assuming the G-R law validity. After contaminating the synthetic catalogues with Gaussian noise (with selected standard deviations), the analysis is performed for numerous data sets of different sample size (N). The noise introduced to the data generally leads to a systematic overestimation of magnitudes close to and above Mc. This fact causes an increase of the average number of events above Mc, which in turn leads to an apparent decrease of the b-value. This may result to a significant overestimation of seismicity rate even well above the actual completeness level. The b-value can in general be reliably estimated even for relatively small data sets (N < 1000) when only magnitudes higher than the actual completeness level are used. Nevertheless, a correction of the total number of events belonging in each magnitude class (i.e. 0.1 unit) should be considered, to deal with the magnitude uncertainty effect. Because magnitude uncertainties (here with the form of Gaussian noise) are inevitable in all instrumental catalogues, this finding is fundamental for seismicity rate and seismic hazard assessment analyses. Also important is that for some data analyses significant bias cannot necessarily be avoided by choosing a high Mc value for analysis. In such cases, there may be a risk of severe miscalculation of seismicity rate regardless the selected magnitude threshold, unless possible bias is properly assessed.

Keywords
Statistical Seismology, Earthquake Catalogue Properties, Completeness Magnitude, b-value
National Category
Earth and Related Environmental Sciences
Research subject
Statistics; Geophysics with specialization in Seismology
Identifiers
urn:nbn:se:uu:diva-328053 (URN)10.1093/gji/ggy023 (DOI)000448720300016 ()
Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2019-01-22Bibliographically approved
Roberts, R., Carbonell, R., Adamaki, A. & Ivandic, M. (2018). Position Document on Future DSS Data Accessibility.
Open this publication in new window or tab >>Position Document on Future DSS Data Accessibility
2018 (English)Report (Other (popular science, discussion, etc.))
Publisher
p. 11
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-358496 (URN)
Projects
SERA
Funder
EU, Horizon 2020, 730900
Available from: 2018-08-29 Created: 2018-08-29 Last updated: 2018-08-30Bibliographically approved
Li, K. L., Sgattoni, G., Sadeghisorkhani, H., Roberts, R. & Gudmundsson, Ó. (2017). A double-correlation tremor-location method. Geophysical Journal International, 208(2), 1231-1236
Open this publication in new window or tab >>A double-correlation tremor-location method
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2017 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 208, no 2, p. 1231-1236Article in journal (Refereed) Published
Abstract [en]

A double-correlation method is introduced to locate tremor sources based on stacks of complex, doubly-correlated tremor records of multiple triplets of seismographs back projected to hypothetical source locations in a geographic grid. Peaks in the resulting stack of moduli are inferred source locations. The stack of the moduli is a robust measure of energy radiated from a point source or point sources even when the velocity information is imprecise. Application to real data shows how double correlation focuses the source mapping compared to the common single correlation approach. Synthetic tests demonstrate the robustness of the method and its resolution limitations which are controlled by the station geometry, the finite frequency of the signal, the quality of the used velocity information and noise level. Both random noise and signal or noise correlated at time shifts that are inconsistent with the assumed velocity structure can be effectively suppressed. Assuming a surface wave velocity, we can constrain the source location even if the surface wave component does not dominate. The method can also in principle be used with body waves in 3-D, although this requires more data and seismographs placed near the source for depth resolution.

Keywords
Correlations, Interferometry, Volcano seismology
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-327035 (URN)10.1093/gji/ggw453 (DOI)000396817600038 ()
Funder
StandUp
Available from: 2017-07-31 Created: 2017-07-31 Last updated: 2018-09-07Bibliographically approved
Wagner, F., Tryggvason, A., Roberts, R. G., Lund, B. & Gudmundsson, Ó. (2017). Automatic seismic event detection using migration and stacking: a performance and parameter study in Hengill, southwest Iceland. Geophysical Journal International, 209(3), 1866-1877
Open this publication in new window or tab >>Automatic seismic event detection using migration and stacking: a performance and parameter study in Hengill, southwest Iceland
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2017 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 209, no 3, p. 1866-1877Article in journal (Refereed) Published
Abstract [en]

We investigate the performance of a seismic event detection algorithm using migration and stacking of seismic traces. The focus lies on determining optimal data dependent detection parameters for a data set from a temporary network in the volcanically active Hengill area, southwest Iceland. We test variations of the short-term average to long-term average and Kurtosis functions, calculated from filtered seismic traces, as input data. With optimal detection parameters, our algorithm identified 94 per cent (219 events) of the events detected by the South Iceland Lowlands (SIL) system, that is, the automatic system routinely used on Iceland, as well as a further 209 events, previously missed. The assessed number of incorrect (false) detections was 25 per cent for our algorithm, which was considerably better than that from SIL (40 per cent). Empirical tests show that well-functioning processing parameters can be effectively selected based on analysis of small, representative subsections of data. Our migration approach is more computationally expensive than some alternatives, but not prohibitively so, and it appears well suited to analysis of large swarms of low magnitude events with interevent times on the order of seconds. It is, therefore, an attractive, practical tool for monitoring of natural or anthropogenic seismicity related to, for example, volcanoes, drilling or fluid injection.

Keywords
Numerical solutions, Time-series analysis, Induced seismicity, Volcano seismology
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-359626 (URN)10.1093/gji/ggx127 (DOI)000408374300036 ()
Funder
Swedish Research Council, 2008:3754
Available from: 2018-09-07 Created: 2018-09-07 Last updated: 2019-02-08Bibliographically approved
Roberts, R., Carbonell, R., Adamaki, A. & Ivandic, M. (2017). Deep Seismic Sounding Data. Zürich: ETH
Open this publication in new window or tab >>Deep Seismic Sounding Data
2017 (English)Report (Other (popular science, discussion, etc.))
Abstract [en]

This document is an interim report within a work package of the SERA project. The document lists a considerable number of previous Deep Seismic Sounding (DSS) projects, where data is available in some form. DSS projects are large scale, logistically complex, and there can be some problems in obtaining formal permission to use the very large seismic sources which may be necessary to be able to successfully record seismic signals penetrating to the relevant depths and distances. This implies that in some cases it would be very difficult to repeat the projects, or conduct a similar project along the same recording profile. This means that even older data can be potentially very valuable, and not all such data is available in modern, digital form (e.g. time series), and some metadata descriptions may be complicated or incomplete.In the text below, we discuss what is meant by DSS data; some of the complications related to this type of data, metadata, different forms of data, and some common types of derived (processed data) which exist. We also present information on a considerable number of DSS projects related to the European area, and list some (but far from all) relevant publications. Note that the term “database” is used in AERA. For DSS data, much data is available in well-structured and maintained digital databases, some is available in digital form only as images of seismic sections, and some data exists only in analogue form e.g. as plotted seismic sections. We consider all such types of data to be relevant, and include them in the “database” concept, as discussed below.

Place, publisher, year, edition, pages
Zürich: ETH, 2017. p. 20
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-358491 (URN)
Projects
SERA
Funder
EU, Horizon 2020, 730900
Available from: 2018-08-29 Created: 2018-08-29 Last updated: 2018-08-30Bibliographically approved
Li, K. L., Sadeghisorkhani, H., Sgattoni, G., Gudmundsson, Ó. & Roberts, R. (2017). Locating tremor using stacked products of correlations. Geophysical Research Letters, 44(7), 3156-3164
Open this publication in new window or tab >>Locating tremor using stacked products of correlations
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2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 7, p. 3156-3164Article in journal (Refereed) Published
Abstract [en]

We introduce a back-projection method to locate tremor sources using products of cross-correlation envelopes of time series between seismic stations. For a given subset of n stations, we calculate the (n - 1)th-order product of cross-correlation envelopes and we stack the back-projected products over combinations of station subsets. We show that compared to existing correlation methods and for realistic signal and noise characteristics, this way of combining information can significantly reduce the effects of correlated (spurious or irrelevant signals) and uncorrelated noise. Each back-projected product constitutes an individual localized estimate of the source locations, as opposed to a hyperbola for the existing correlation techniques, assuming a uniform velocity in two dimensions. We demonstrate the method with synthetic examples and a real-data example from tremor at Katla Volcano, Iceland, in July 2011. Despite very complex near-surface structure, including strong topography and thick ice cover, the method appears to produce robust estimates of tremor location.

Keywords
correlation, volcanic tremor, tremor location, source location, interferometry
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-322813 (URN)10.1002/2016GL072272 (DOI)000400186500022 ()
Available from: 2017-06-08 Created: 2017-06-08 Last updated: 2017-08-01
Projects
SubCity: Future imaginaries of the city subsurface [2020-00048_Formas]; Uppsala University; Publications
Kuchler, M., Craig-Thompson, A., Alofe, E. & Tryggvason, A. (2024). SubCity: Planning for a sustainable subsurface in Stockholm. Tunnelling and Underground Space Technology, 144, 105545, Article ID 105545.
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7251-0059

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