Paleogeophysics and Geodynamics Institute
Recent publications
Large magnitude (Mw ∼ ≥6) earthquakes in extensional settings are often associated with simultaneous rupture of multiple normal faults as a result of static and/or dynamic stress transfer. Here, we report details of the coseismic breaching of a previously unrecognized large‐scale fault relay zone in central Greece, through three successive normal fault earthquakes of moderate magnitude (Mw 5.7–6.3) that occurred over a period of ∼10 days in March 2021. Specifically, joint analysis of InSAR, GNSS and seismological data, coupled with detailed field and digital fault mapping, reveals that the Tyrnavos Earthquake Sequence (TES) was accommodated at the northern end of a ∼100 km wide transfer structure, by faults largely unbroken during the Holocene. By contrast, the southern section of this relay zone appears to have accrued significant slip during Holocene. InSAR‐derived displacements agree with the loci of eight subtle, previously undetected, faults that accommodated coseismic and/or syn‐seismic normal fault slip during the TES. Kinematic modeling coupled with fault mapping suggests that all involved faults are interconnected at depth, with their conjugate fault‐intersections acting largely as barriers to coseismic rupture propagation. We also find that the TES mainshocks were characterized by unusually high (>6 MPa) stress‐drop values that scale inversely with rupture length and earthquake magnitude. These findings, collectively suggest that the TES propagated north‐westward to rupture increasingly stronger asperities at fault intersections, transferring slip between the tips of a well‐established, but previously unrecognized, relay structure. Fault relay zones may be prone to high stress‐drop earthquakes and associated elevated seismic hazard.
Sweden has thousands of caves cut into the bedrock, two thirds of which occur in the crystalline bedrock, and hence represent pseudokarst phenomena. The formation of these caves can only be understood in terms of paleoseismics. In this paper, we review the parallel evolution of the concept of pseudokarst caves and of the concept of paleoseismic activity in Sweden, and combine both concepts into a unified theory on the formation of fractures, fracture caves and angular block heaps.
The anomalous pattern of relative sea levels for the Samoan Islands that followed the 2009 earthquake and tsunami is explained by coupling tide-gauge time series of relative sea levels and GPS time series of absolute geocentric positions of inland fixed domes. The subsidence of the land is responsible for the relative sea level acceleration that followed the earthquake. The pattern of subsidence is characterized by small departures from a linear pattern immediately before the earthquake, an abrupt change at the earthquake, and then a parabolically reducing extra subsidence. The absolute geocentric sea levels obtained clearing the relative sea level signal of the subsidence signal are stable. There is a need to couple GPS monitoring of tide gauge position with tide gauge measurements of relative sea levels without any linearity assumption to produce reliable, accurate, assessments of the pattern of sea level rise to inform policy makers.
A moderate, shallow depth, earthquake (Mw = 6.5) occurred onshore Lefkada island on November 17, 2015 with the focal depth estimated at 11 km. The seismic fault is a near-vertical strike-slip fault running along the western coast, part of the Cephalonia Transform Fault. Landslides and ground cracks were mainly reported at the western part of the island, inducing structural damages. High severity slope failures occurred at Egremnoi and Gialos areas that both are located at coastal regions. This study aims to investigate the engineering geological conditions at these areas, and assess the characteristics and physical quantities (e.g., type, area—m2, and volume—m3) of the instabilities. To achieve this, engineering geological mapping was implemented in Egremnoi and Gialos area aiming to; (a) classify the geological units mapped on the heavily damaged areas and (b) to correlate them with the type of slope failures. Furthermore, type and dimensions of slope failures were evaluated to estimate the total volume of the mass movement. All the data, originated from the engineering geological mapping, have been digitized and rasterized at 5 m grid spacing using the Arc/Info GIS software to perform a Newmark’s sliding block analysis. The outcome arisen by this analysis is that the generated by the earthquake peak ground acceleration at these areas should be at least 0.45 g to trigger these kinds of slope failures.
Mörner, N.-A., 0000. Coastal morphology and sea-level changes in Goa, India during the last 500 years. Coastal morphology, stratigraphy, radiocarbon dating, archaeological remains, historical documentation, and tide gauge records allowed us to establish a very firm and detailed record of the changes in sea level in Goa over the last 500 years. It is an oscillation record: a low level in the early 16th century, a +50-cm high level in the 17th century, a level below present sea level in the 18th century, a +20-cm high level in the 19th and early 20th centuries, a ∼20-cm fall in 1955–1962, and a virtually stable level over the last 50 years. This sea level record is almost identical to those obtained in the Maldives and in Bangladesh. The Indian Ocean seems to lack records of any alarming sea-level rise in recent decades; on the contrary, 10 sites analyzed indicate a sea level remaining at about ±0.0, at least over the last 50 years or so.
Seismology and palaeoseismology have a mutual goal in the assessment of seismic hazards. They are both needed to make the assessments meaningful. There are, however, some dialectics between the two disciplines. The south Scandinavian situation is highlighted with respect to the questions of seismic continuity versus discontinuity, coincidence versus verification and the application of multiple parameters in palaeoseismology. It is concluded that millennial-scale seismic records are characterized by discontinuities in seismic activity. In southern Scandinavia there is a clear successive increase in the maximum earthquake moment magnitudes back in time from <4.5 today, via >6 to c. 7 in the Late Holocene to c. 8 to >8 during times of deglaciation. This paper presents a rather philosophical view of the dialectics and interactions between instrumental seismology and geologically based palaeoseismology. This means that it is strongly based on the author's own material in the field and his mind because it represents his own experiences over a long period of active work in palaeoseismology and neotectonics.
Ales Stones is a 67 m long stone ship in SE Sweden. It possesses strict alignments with respect to the annual motions of the Sun. It also records the months and days of the year, and the time of the day. It seems likely that it was erected as a calendar and sundial. Its age has been debated. It is now possible to assign a proper age of the erection of the monument. Several converging facts indicate an age of the Late Bronze Age of about 750–800 BC.
Coastal erosion is caused by many different processes like changes in prevailing wind direction, coastal currents, re-establishment of a new equilibrium profile, sea level rise, sea level fall, exceptional storms, hurricanes/cyclones, and tsunami events. These coastal factors are reviewed with special attention to effects due to changes in sea level. In the Indian Ocean, sea level seems to have remained virtually stable over the last 40-50 years. Coastal erosion in the Maldives was caused by a short lowering in sea level in the 1970s. In Bangladesh, repeated disastrous cyclone events cause severe coastal erosion, which hence has nothing to do with any proposed sea level rise. Places like Tuvalu, Kiribati and Vanuatu – all notorious for an inferred sea level rise – have tide gauges, which show no on-going sea level rise. Erosion is by no means a sign of sea level rise. Coastal erosion occurs in uplifting regions as well as in subsiding regions, or virtually stable areas. Coastal morphology provides excellent insights to the stability. The coastal characteristics tell us about sea level changes, changes in prevailing wind and currents, and the occurrence of storms, hurricanes and tsunamis. Erosion in one part of a coastline implies deposition in another. The formation of a shoreline (notch, terrace, rock cut platform, beach ridge, coastal bar, etc.) takes time. Therefore, most of the prominent fossil shorelines (uplifted above sea level as well as submerged below sea level) represent halts or oscillations in the general postglacial rise of sea level.
It has been possible to document seveal paleoseismic events in Sweden in the period at around the deglaciation. A major earthquake occurred in the autumn of varve 10,430 BP. It generated liquefaction over 320 km. Another event occurred in varve 9663 BP It generated seismites over a distance of 210 km. Both events also generated tsunamis. The tsunami wave of the 10,430-event washed the strait between the Baltic and the North Sea free of ice so that marine water suddenly could invade the Baltic basin creating the so-called Yoldia Sea stage. The 9663-event set up a tsunami wave recorded in the ice marginal sedimentology and shore morphology in such details that it seems possible to record a triple deformation/flow sequence.
At about 780-750 BC, a major earthquake struck southeast Sweden. At Branteträsk, the bedrock of quartzite was heavily fractured into big, flat blocks. Local people turned the site into a quarry for flat blocks to be placed around the Late Bronze Age graves at Brantevik, the big flat blocks of the sarcophagus, and two 5 tons monoliths transported 30 km to the SSW and erected as the bow and stern stones in the huge ship monument of Ales Stones. Rock carvings from the Bronze Age at Jär-restad became traversed by numerous fractures. Similar rock carving fracturing was observed at six other sites within a radius of 5 km from Branteträsk. In the shore cliff at Ales Stones a seismite was recorded and dated at 780-750 BC. At Glimme hallar, 4 km WSW of Brantevik, the bedrock shows signs of young tectonization. At Lillehem, 40 km to the NNW of Branteträsk, seismically disturbed beds were recorded and dated at the Late Holocene. The seismic event is concluded to have occurred around 780-750 cal.yrs BC and to have had a magnitude in the order of 6.3 to 6.8 and an intensity of about IX on the IES scale.
In a collection of research papers devoted to the problem of solar variability and its origin in plan-etary beat, it is demonstrated that the forcing function originates from gravitational and inertial effects on the Sun from the planets and their satellites. This conclusion is shared by nineteen co-authors.
The Swedish Varve Chronology initiated by De Geer, and revised and updated by several successors, offers the possibility to test the synchroneity of deformations and turbidites. There are many examples of synchronous deformations over wide areas. This calls for an explanation in terms of ground shaking by high-magnitude earthquakes. Several well-known varve events previously interpreted as “drainage varves” are shown here to be seismically induced marker-beds. Therefore they should be renamed as seismites. Some are, in fact, formed by tsunami waves, and should be termed tsunamites. By this, the Swedish Time Scale becomes a very useful archive for the identification and dating of palaeoseismic events.
Introduction to our special issue on Patterns in Solar variability, their origins and terrestrial impacts. Investigations of the hypothesis of a planetary affect on solar variability confirms strong correlations between planetary motion and solar activity changes. These are visible in Earth's paleological history proxy records and contemporary direct measurements.
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Uppsala, Sweden