The devastating effects caused by the recent catastrophic earthquakes that took place all over the world from Japan, New Zealand, to Chile, as well as those occurring in the Mediterranean basin, have ...once again shown that ground motion, although a serious source of direct damage, is not the only parameter to be considered, with most damage being the result of coseismic geological effects that are directly connected to the earthquake source or caused by ground shaking. The primary environmental effects induced by earthquakes as well as the secondary effects (sensu Environmental Seismic Intensity - ESI 2007 scale) must be considered for a more correct and complete evaluation of seismic hazards, at both regional and local scales. This Special Issue aims to collect all contributions that, using different methodologies, integrate new data produced with multi-disciplinary and innovative methods. These methodologies are essential for the identification and characterization of seismically active areas, and for the development of new hazard models, obtained using different survey techniques. The topic attracted a lot of interest, 19 peer-reviewed articles were collected; moreover, different areas of the world have been analyzed through these methodologies: Italy, USA, Spain, Australia, Ecuador, Guatemala, South Korea, Kyrgyzstan, Mongolia, Russia, China, Japan, and Nepal.
We digitize surface rupture maps and compile observational data from 67 publications on ten of eleven historical, surface-rupturing earthquakes in Australia in order to analyze the prevailing ...characteristics of surface ruptures and other environmental effects in this crystalline basement-dominated intraplate environment. The studied earthquakes occurred between 1968 and 2018, and range in moment magnitude (Mw) from 4.7 to 6.6. All earthquakes involved co-seismic reverse faulting (with varying amounts of strike-slip) on single or multiple (1–6) discrete faults of ≥ 1 km length that are distinguished by orientation and kinematic criteria. Nine of ten earthquakes have surface-rupturing fault orientations that align with prevailing linear anomalies in geophysical (gravity and magnetic) data and bedrock structure (foliations and/or quartz veins and/or intrusive boundaries and/or pre-existing faults), indicating strong control of inherited crustal structure on contemporary faulting. Rupture kinematics are consistent with horizontal shortening driven by regional trajectories of horizontal compressive stress. The lack of precision in seismological data prohibits the assessment of whether surface ruptures project to hypocentral locations via contiguous, planar principal slip zones or whether rupture segmentation occurs between seismogenic depths and the surface. Rupture centroids of 1–4 km in depth indicate predominantly shallow seismic moment release. No studied earthquakes have unambiguous geological evidence for preceding surface-rupturing earthquakes on the same faults and five earthquakes contain evidence of absence of preceding ruptures since the late Pleistocene, collectively highlighting the challenge of using mapped active faults to predict future seismic hazards. Estimated maximum fault slip rates are 0.2–9.1 m Myr−1 with at least one order of uncertainty. New estimates for rupture length, fault dip, and coseismic net slip can be used to improve future iterations of earthquake magnitude—source size—displacement scaling equations. Observed environmental effects include primary surface rupture, secondary fracture/cracks, fissures, rock falls, ground-water anomalies, vegetation damage, sand-blows/liquefaction, displaced rock fragments, and holes from collapsible soil failure, at maximum estimated epicentral distances ranging from 0 to ~250 km. ESI-07 intensity-scale estimates range by ± 3 classes in each earthquake, depending on the effect considered. Comparing Mw-ESI relationships across geologically diverse environments is a fruitful avenue for future research.
Landslide size controls the destructive power of landslides and is related to the frequency of occurrence, with larger landslides being less frequent than smaller ones. For this reason, the analysis ...of landslide size is essential for landslide hazard assessment. We analyse six earthquake-induced landslide inventories with earthquake magnitude ranging between 6.6 and 7.9 Mw (Papua New Guinea, 1993; ChiChi 1999; Northridge, 1994; Niigata–Chuetsu, 2004; Iwate–Miyagi Nairiku, 2008; Wenchuan, 2008). For each inventory, we developed magnitude–frequency curves to analyse the size distribution of landslides as a function of ground motion, distance from the seismic source (both fault trace and epicentre), local relief, and lithology. For three earthquakes, we observed a clear relationship between the landslide size and ground motion, with larger landslides associated with higher ground motion. We investigate different possible causes for such observation, and propose that the main mechanical reason is that stronger shaking induces higher stresses that may overcome the strength, which increases with depth, triggering larger landslides. We also show that landslide size decreases with distance from the fault trace, whereas, this trend is not clear for distance from the epicentre. Local relief does not seem a first order control on landslide size for the earthquake-induced landslides considered here. Some lithologies do influence landslide size, but we were unable to identify a general behaviour for different lithologies.
•Ground motion modulates landslide size on a given landscape, with a tendency of larger landslides with stronger ground motion.•The relative abundance of larger landslides decreases moving away from the seismic faults trace.•The influence of ground motion on landslide size may be affected by local morphological and lithological conditions.
Earthquake-induced landslides can cause enormous damage and numerous casualties in mountainous areas worldwide; consequently, accurate assessment of the potential distribution of earthquake-induced ...landslides is an important issue. For a national disaster prevention agency, it is desirable to be prepared to rapidly evaluate disasters and risks from information that can be scarce or easily available. The present study examined landslides triggered by reverse and strike-slip fault earthquakes, focusing on recent cases in Japan with relatively complete landslide inventories and detailed active-fault information. The landslide distributions and parameters of active faults were compared, and it was found that the skewness and kurtosis of the landslide distribution for each earthquake event was close to zero, indicating that the distributions followed the normal distribution. The mean distance of the landslide distribution from the active fault is negatively correlated with the inclination of the active fault, while the standard deviation is negatively correlated with the fault-top depth of the active fault and positively correlated with the magnitude of the earthquake.
Based on our findings, we conducted a regression analysis of the relationship between the mean distance from the active fault and the inclination of the active fault. The mean distance of the landslide from the active fault increased when the active fault had a lower inclination, and was regarded as zero when the inclination was greater than 60°. In addition, a relationship between the standard deviation, depth of fault top, and earthquake magnitude was established using multiple regression analysis. We thus confirmed the accuracy of the methodology using the actual landslide distributions of recent earthquakes in Japan. The length of the active fault can be used as input for the methodology, to estimate the maximum magnitude of the respective earthquake. Furthermore, the 95% confidence interval appears to cover almost all the large landslides, which enables us to limit the extent of areas that should be considered as the most exposed to co-seismic landslide hazards. The applicability of the proposed methodology was successfully tested using the case of the 1999 Chi-Chi earthquake in Taiwan with a seismic mechanism similar to the Japanese earthquake. Consequently, the proposed methodology can be applied to estimate the potential distribution of landslides caused by reverse and strike-slip fault earthquakes, based on the parameters of the active faults.
•The distribution of earthquake-induced landslides follows a normal distribution.•The fault's inclination affects the mean distance between landslides and the fault.•The SD of distance between landslides and the fault is controlled by EQ magnitude.•The 95% confidence interval of the normal distribution covers most large landslides.
•Slow earthquakes were complementarily distributed along the Nankai megathrust.•Their activities are characterized by migration in deep & shallow plate boundaries.•Deep and shallow migrations ...occurred over 2–3 years & ∼1 month, respectively.•Both migrating phenomena propagate ∼300 km towards the Nankai locked area.
The Nankai megathrust is located offshore Shikoku and Kyushu, Japan and is characterized by various kinds of slow earthquakes whose relative motions across the plate boundary faults are slower than regular earthquakes. In the area, the interplate locking is stronger in the northern area (offshore Shikoku) than in the southern area (offshore Kyushu) and Mw ∼8 earthquakes (Nankai earthquakes) have occurred repeatedly in the northern area. In this paper, the spatio-temporal distributions of slow earthquakes (very low frequency earthquakes, tremors and slow-slip events) are examined based on the analyses of repeating earthquakes and slow earthquakes with special focus on the interaction between different activities. A comprehensive analysis of the seismic and geodetic data from 2003 to 2016 indicates complementary distribution of various types of slow earthquakes down to 35–50 km depth outside the Nankai main locking area. We also found interactions between different kinds of activities. The interactions between the repeating earthquakes and slow earthquakes suggest that the area of the repeating earthquakes activity can be divided into deeper (depth ≥ 20 km) and shallower (depth < 20 km) areas. The analyses of deep repeating earthquakes and the inland Global Navigation Satellite System (GNSS) data suggests slow northward migrations of long-term slow slip events (SSEs) in 20–50 km (offshore Kyushu) and 20–35 km (under Shikoku) depths along the plate boundary. These migrations occurred during a period of 2–3 years that includes the 2003 and 2010 large slow-slip events in the Bungo channel located in between Kyushu and Shikoku. The analysis has also shown interaction between shallow repeating earthquakes and shallow very low frequency earthquakes which indicates faster northward migrations of short-term SSEs from the shallow plate boundary offshore Kyushu to the deeper area under Shikoku over the duration of a month during the 2010 long-term slow-slip episode. The deep slow migration and the shallow to deep fast migration of SSEs in a ∼300 km area towards and around the source area of the recurrent Nankai earthquake (Mw 8.0–8.6) indicates the occurrence of a widespread non-steady stress build-up process around the source area of the Nankai megathrust earthquake.
Landward increase of surface velocity has been found for segments adjacent along-strike to megathrust faults after the 2003 Tokachi-oki and the 2011 Tohoku-oki earthquakes, NE Japan. A similar ...increase of landward velocities was reported for the segments to the north of the rupture of the 2010 Maule earthquake, Chile. We utilize available GNSS data to find such changes for six megathrust earthquakes in four subduction zones, including NE Japan, central and northern Chile, Sumatra, and Mexico to investigate their common features. Our study showed that such increase, ranging from a few mm/yr to ~1 cm/yr, appeared in adjacent segments following the 2014 Iquique (Chile), the 2007 Bengkulu (Sumatra), and the 2012 Oaxaca (Mexico) earthquakes in addition to the three cases. The region of the increased landward movements extends with spatial decay and reach the distance comparable to the along-strike fault length. On the other hand, the temporal decay of the increased velocity is not clear at present. The degree of increase seems to depend on the earthquake magnitude, and possibly scales with the average fault slip in the earthquake. This is consistent with the simple two-dimensional model proposed earlier to attribute the phenomenon to the enhanced coupling caused by accelerated subduction. However, these data are not strong enough to rule out other possibilities.
•We found landward velocity increases of adjacent segments in 4 different subduction zones after 6 megathrust earthquakes.•The area showing such landward increase extends along-strike with clear spatial decay.•The increased state continues with little temporal decay.•The velocity increase may scale with the coseismic fault slip.
Intersecting orthogonal strike‐slip faults with opposite senses of slip pose the question of what allows rupture to propagate through the junction and through both faults versus confining rupture to ...a single fault. I conduct dynamic rupture simulations on simplified orthogonal strike‐slip fault systems, to determine which conditions produce rupture on both component faults. In models with uniform initial tractions on both faults, slip on the first fault must reduce normal stress on the second fault for it to rupture. If the first fault ends at the cross fault, a stopping phase causes the cross fault to rupture. In models where I resolve a uniform regional stress field on the faults, only a narrow range of stress orientations allow multifault ruptures. These results will be helpful for evaluating hazard near orthogonal strike‐slip faults.
Plain Language Summary
There are many examples around the world where two strike‐slip earthquake faults cross each other at nearly 90° angles. This is not remarkable when only one of the faults in a pair causes an earthquake, but it becomes notable when two or more crossing faults move at the same time. This raises the question of what causes the second fault to get involved, or not. To address this question, I use computer simulations of the physics of the earthquake process to test dozens of different fault configurations and earthquake starting points. I find that the location where the earthquake starts on the first fault controls whether the second fault is made stronger versus weaker, and therefore whether both faults can move together in one earthquake. These results can help us understand earthquake hazard around crossing faults.
Key Points
Nucleation location effectively controls whether multifault rupture occurs on orthogonal strike‐slip fault systems
A stopping phase from rupture reaching the end of one fault is often required to initiate rupture on the cross fault
Only a narrow range of regional stress orientations allows both cross‐faults to rupture
This paper investigates the effect of earthquake ground motion duration on the design and collapse risk of reinforced concrete shear wall buildings from 6 to 30 stories. Both design and collapse ...levels of shaking were considered through nonlinear incremental dynamic analysis. At the design level of shaking, it was found that (1) maximum interstory drifts were increased as ground motion duration increased (from <20 s to 35-150 s of strong shaking), though not enough to flag the designs as unacceptable; (2) story forces and moments were not significantly affected; and (3) energy demands were greatly increased by motion duration. When the records were scaled until collapse level, it was found that (1) the median collapse scaling level was greatly impacted by duration, and the median collapse shaking level was almost 20% higher on average when considering shorter records; and (2) long duration records produced both larger probabilities of collapse at the design shaking level and lower collapse margin ratios compared with spectrally equivalent short duration records.
Subduction zone plate boundary megathrust faults accommodate relative plate motions with spatially varying sliding behavior. The 2004 Sumatra‐Andaman (Mw 9.2), 2010 Chile (Mw 8.8), and 2011 Tohoku ...(Mw9.0) great earthquakes had similar depth variations in seismic wave radiation across their wide rupture zones – coherent teleseismic short‐period radiation preferentially emanated from the deeper portion of the megathrusts whereas the largest fault displacements occurred at shallower depths but produced relatively little coherent short‐period radiation. We represent these and other depth‐varying seismic characteristics with four distinct failure domains extending along the megathrust from the trench to the downdip edge of the seismogenic zone. We designate the portion of the megathrust less than 15 km below the ocean surface as domain A, the region of tsunami earthquakes. From 15 to ∼35 km deep, large earthquake displacements occur over large‐scale regions with only modest coherent short‐period radiation, in what we designate as domain B. Rupture of smaller isolated megathrust patches dominate in domain C, which extends from ∼35 to 55 km deep. These isolated patches produce bursts of coherent short‐period energy both in great ruptures and in smaller, sometimes repeating, moderate‐size events. For the 2011 Tohoku earthquake, the sites of coherent teleseismic short‐period radiation are close to areas where local strong ground motions originated. Domain D, found at depths of 30–45 km in subduction zones where relatively young oceanic lithosphere is being underthrust with shallow plate dip, is represented by the occurrence of low‐frequency earthquakes, seismic tremor, and slow slip events in a transition zone to stable sliding or ductile flow below the seismogenic zone.
Key Points
Seismic radiation from megathrust earthquake rupture varies with depth
A 4‐domain model of radiation segmentation is introduced for megathrusts
Strong‐ground motions originate from the down‐dip region
Repeating Earthquakes Uchida, Naoki; Bürgmann, Roland
Annual review of earth and planetary sciences,
05/2019, Volume:
47, Issue:
1
Journal Article
Peer reviewed
Repeating earthquakes, or repeaters, are identical in location and geometry but occur at different times. They appear to represent recurring seismic energy release from distinct structures such as ...slip on a fault patch. Repeaters are most commonly found on creeping plate boundary faults, where seismic patches are loaded by surrounding slow slip, and they can be used to track fault creep at depth. Their hosting environments also include volcanoes, subducted slabs, mining-induced fault structures, glaciers, and landslides. While true repeaters should have identical seismic waveforms, small differences in their seismograms can be used to examine subtle changes in source properties or in material properties of the rocks through which the waves propagate. Source studies have documented the presence of smaller slip patches within the rupture areas of larger repeaters, illuminated earthquake triggering mechanisms, and revealed systematic changes in rupture characteristics as a function of loading rate.
Repeating earthquakes are observed in diverse tectonic and nontectonic settings.
Their occurrence patterns provide quantitative information about fault creep, earthquake cycle dynamics, triggering, and predictability.
Their seismic waveform characteristics provide important insights on earthquake source variability and temporal Earth structure changes.
PDF
