Archaeoseismic Evidence of Surface Faulting in 1703 Norcia Earthquake (Central Italian Apennines, Mw 6.9)

We present the first evidence of surface rupture along the causative fault of the 14 January 1703 earthquake (Mw 6.9, Italian central Apennines). This event was sourced by the ~30 km-long, Norcia fault system, responsible for another catastrophic event in Roman times, besides several destructive earthquakes in the last millennium. A dozen paleoseismological excavations have already investigated the surface ruptures occurred during the Holocene along the Cascia-Mt Alvagnano segments, as well as along secondary splays close to the Medieval Norcia Walls. Remarkably, the master fault bounding the Norcia-Campi basins have never be proved to rupture at the surface. An antique limekiln that was improvidently set across the main fault scarp provides the amazing evidence of an abrupt offset in the 1703 earthquake, which likely occurred during a liming process of carbonate stones. Obviously, the limekiln became useless, and was progressively buried by slope debris. The amount of the offset and the kinematics indicators surveyed in the site allow the strengthening of our knowledge on the seismogenic potential of the Norcia fault system, on its geomorphic rule, and on its impact on the human activities.

Geomorphological Analysis of Xilokastro Fault, Central Gulf of Corinth, Greece

The Gulf of Corinth is a rapidly opening area with high seismicity associated with extensive building collapses, destruction of cities, and even the deaths of inhabitants. Rapid residential development, especially in the southern part of the Gulf of Corinth, and the construction of crucial technical infrastructures necessitate understanding the activity across crustal-scale faults that host devastating earthquakes. The evolution of landforms affected by fault action is a dominant issue in geological science. In the present study, was selected the 20 km long Xilokastro pure normal fault. In this fault, we apply eight geomorphological indices in footwall catchments that drain perpendicular to its trace. In total, more than 5000 measurements were made in 102 catchments. The determination of geomorphological indices requires the construction of morphological profiles either perpendicular to the faults or perpendicular to the main tributaries of the drainage basins under consideration through the use of the geographical information systems (ArcGIS platform). Τhe application of these indices along catchments draining the Xilokastro fault scarp show high active tectonics. Its high activity is evidenced by the high values of the length-slope index near the fault trace, the low values of the width to height ratio index, the strong asymmetry of the drainage basins, especially in the overlapping zones between its segments, and the elongated shape of the drainage basins. This study supports the idea that the application of a single morphometric index is unable to reflect the distribution of active tectonics across faults, which makes inevitable the systematic comparison of a series of tectonic morphometric indices from which a new combined index emerges (Iat). The Iat classifies the Xilokastro fault in the high degree of activity at a rate of 75% of its length.

Using Structural Geology and Cosmogenic Nuclide Dating to Infer the Slip Rate and Frictional Strength of the Active Mai’iu Low-Angle Normal Fault, Eastern Papua New Guinea

<p>Low-angle normal faults (LANFs) have induced debate due to their apparent non -Andersonian behaviour and lack of significant seismicity associated with slip. Dipping 21°/N, the Mai’iu Fault, located in the Woodlark Rift, Eastern Papua New Guinea is an active LANF that occupies a position at the transition between continental extension and seafloor spreading. Surface geomorphology indicates that the Mai’iu Fault scarp is not significantly eroded despite high rainfall and ~2900 m of relief. Based on modelling of regional campaign GPS data (Wallace et al., 2014) the Mai’iu Fault is thought to accommodate rapid (7–9 mm/yr) horizontal extension; however the slip rate of the Mai’iu Fault has not been directly validated. I use a range of methodologies, including field mapping, cosmogenic exposure dating, cosmogenic burial dating, and Mohr-Coulomb modelling, in order to provide new constraints on LANF strength and slip behaviour. I analyse the structure of conglomeratic strata within a back -rotated rider block atop the Mai’iu Fault surface. The Gwoira rider block is a large fault-bounded sedimentary rock slice comprising the Gwoira Conglomerate, located within a large synformal megamullion in the Mai’iu Fault surface. The Gwoira Conglomerate was originally deposited on the Mai’iu Fault hanging wall concurrent with extension, and has since been buried to a maximum depth of ~2 km (evidenced by modelling of vitrinite reflectance data, and structural analysis), back-tilted, and synformally folded. The Mai’iu Fault is also overlain by a large fault slice (the Gwoira rider block), that has been transferred from the previous LANF hanging wall to the current footwall by the initiation of the younger Gwoira Fault. Both the Gwoira Conglomerate (former hanging wall) and mylonitic foliation (footwall) of the Mai’iu Fault have been shortened ~E-W, perpendicular to the extension direction. I show that N-S trending synformal folding of the Gwoira Conglomerate was concurrent with on-going sedimentation and extension on the Mai’iu Fault. Structurally shallower Gwoira Conglomerate strata are folded less than deeper strata, indicating that folding was progressively accrued concurrent with ~N -S extension. I also show that abandonment of the inactive strand of the Mai’iu Fault in favour of the Gwoira Fault, which resulted in formation of the Gwoira rider block, occurred in response to progressive megamullion amplification and resultant misorientation of the inactive strand of the Mai’iu Fault. I attribute N-S trending synformal folding to extension-perpendicular constriction. This is consistent with numerous observations of outcrop-scale conjugate strike-slip faults that deform the footwall and hanging wall of the Mai’iu Fault (Little et al., 2015), and accommodate E-W shortening. Constrictional folding remains active in the near-surface as evidenced by synformal tilting of inferred Late Quaternary fluvial terraces atop the Gwoira rider block. In order to date this sequence of progressive constrictional folding, I have processed ten ²⁶Al/¹⁰Be terrestrial cosmogenic nuclide burial samples obtained from the Gwoira Conglomerate; unfortunately these data were not yet available at the time of printing, due to reasons outside of my control. I also present terrestrial cosmogenic nuclide (TCN) exposure ages for ten rock samples obtained from the lowermost Mai’iu Fault scarp at Biniguni Falls, in order to determine the Holocene slip-rate and style using cosmogenic ¹⁰Be in quartz. I model exposure age data after the approach of Schlagenhauf et al. (2011), using a Monte-Carlo simulation in which fault slip rate, the period of last slip on the fault, and local erosion rate are allowed to vary. Modelling evidences that the Mai’iu Fault at Biniguni Falls is active and slipping at 13.9±4.0 mm/yr (1σ), resolved over the last 13.2±2.7 ka (1σ). Modelling constrains the time of last slip to 2.9±1.4 ka (1σ); this is consistent with a seismic event at that time, followed by non-slip on the Mai’iu Fault until the present day. Finally, because rider block formation records abandonment of the uppermost part of a LANF, Coulomb fault mechanical analysis can be applied to field observations to provide an upper limit on LANF frictional strength (µf). Calculations are made in terms of Mohr-Coulomb mechanics, after the framework of Choi and Buck (2012). The lock-up (abandonment) orientation at any particular position on the Mai’iu Fault is principally a function of fault friction (µf), crustal friction (µc), fault cohesion (Cf), crustal cohesion (Cc), depth, fault orientation, fluid pressure, and the orientation of the greatest principle stress. Model results suggest that fault friction for the active Gwoira-Mai’iu Fault surface is 0.128≤μf≤0.265 for Cf<1.8 MPa, and 0.2≤μf≤0.265 for Cf≤0.5 MPa. Modelling of abandonment of the inactive Mai’iu Fault suggests that 0.26≤μf≤0.309 for Cf<1.8 MPa. This suggests that past slip on the inactive Mai’iu Fault, and continued slip on the active Gwoira-Mai’iu Fault, were enabled by low fault frictional strength. I also model the strength of the active Mai’iu Fault at Biniguni Falls; results suggest greater LANF friction (μf≥0.32) than the Gwoira-Mai’iu Fault surface, and inactive Mai’iu Fault. In order to explain active slip on the LANF at Biniguni Falls concurrent with widespread field observations of outcrop-scale faulting of the LANF footwall, I suggest a process whereby overall the LANF remains viable and active, but locally stress conditions exceed the LANF abandonment criteria; this results in highly localised and temporary ‘footwall damage’ where the LANF footwall is locally dissected by outcrop-scale faulting.</p>

Using Structural Geology and Cosmogenic Nuclide Dating to Infer the Slip Rate and Frictional Strength of the Active Mai’iu Low-Angle Normal Fault, Eastern Papua New Guinea

<p>Low-angle normal faults (LANFs) have induced debate due to their apparent non -Andersonian behaviour and lack of significant seismicity associated with slip. Dipping 21°/N, the Mai’iu Fault, located in the Woodlark Rift, Eastern Papua New Guinea is an active LANF that occupies a position at the transition between continental extension and seafloor spreading. Surface geomorphology indicates that the Mai’iu Fault scarp is not significantly eroded despite high rainfall and ~2900 m of relief. Based on modelling of regional campaign GPS data (Wallace et al., 2014) the Mai’iu Fault is thought to accommodate rapid (7–9 mm/yr) horizontal extension; however the slip rate of the Mai’iu Fault has not been directly validated. I use a range of methodologies, including field mapping, cosmogenic exposure dating, cosmogenic burial dating, and Mohr-Coulomb modelling, in order to provide new constraints on LANF strength and slip behaviour. I analyse the structure of conglomeratic strata within a back -rotated rider block atop the Mai’iu Fault surface. The Gwoira rider block is a large fault-bounded sedimentary rock slice comprising the Gwoira Conglomerate, located within a large synformal megamullion in the Mai’iu Fault surface. The Gwoira Conglomerate was originally deposited on the Mai’iu Fault hanging wall concurrent with extension, and has since been buried to a maximum depth of ~2 km (evidenced by modelling of vitrinite reflectance data, and structural analysis), back-tilted, and synformally folded. The Mai’iu Fault is also overlain by a large fault slice (the Gwoira rider block), that has been transferred from the previous LANF hanging wall to the current footwall by the initiation of the younger Gwoira Fault. Both the Gwoira Conglomerate (former hanging wall) and mylonitic foliation (footwall) of the Mai’iu Fault have been shortened ~E-W, perpendicular to the extension direction. I show that N-S trending synformal folding of the Gwoira Conglomerate was concurrent with on-going sedimentation and extension on the Mai’iu Fault. Structurally shallower Gwoira Conglomerate strata are folded less than deeper strata, indicating that folding was progressively accrued concurrent with ~N -S extension. I also show that abandonment of the inactive strand of the Mai’iu Fault in favour of the Gwoira Fault, which resulted in formation of the Gwoira rider block, occurred in response to progressive megamullion amplification and resultant misorientation of the inactive strand of the Mai’iu Fault. I attribute N-S trending synformal folding to extension-perpendicular constriction. This is consistent with numerous observations of outcrop-scale conjugate strike-slip faults that deform the footwall and hanging wall of the Mai’iu Fault (Little et al., 2015), and accommodate E-W shortening. Constrictional folding remains active in the near-surface as evidenced by synformal tilting of inferred Late Quaternary fluvial terraces atop the Gwoira rider block. In order to date this sequence of progressive constrictional folding, I have processed ten ²⁶Al/¹⁰Be terrestrial cosmogenic nuclide burial samples obtained from the Gwoira Conglomerate; unfortunately these data were not yet available at the time of printing, due to reasons outside of my control. I also present terrestrial cosmogenic nuclide (TCN) exposure ages for ten rock samples obtained from the lowermost Mai’iu Fault scarp at Biniguni Falls, in order to determine the Holocene slip-rate and style using cosmogenic ¹⁰Be in quartz. I model exposure age data after the approach of Schlagenhauf et al. (2011), using a Monte-Carlo simulation in which fault slip rate, the period of last slip on the fault, and local erosion rate are allowed to vary. Modelling evidences that the Mai’iu Fault at Biniguni Falls is active and slipping at 13.9±4.0 mm/yr (1σ), resolved over the last 13.2±2.7 ka (1σ). Modelling constrains the time of last slip to 2.9±1.4 ka (1σ); this is consistent with a seismic event at that time, followed by non-slip on the Mai’iu Fault until the present day. Finally, because rider block formation records abandonment of the uppermost part of a LANF, Coulomb fault mechanical analysis can be applied to field observations to provide an upper limit on LANF frictional strength (µf). Calculations are made in terms of Mohr-Coulomb mechanics, after the framework of Choi and Buck (2012). The lock-up (abandonment) orientation at any particular position on the Mai’iu Fault is principally a function of fault friction (µf), crustal friction (µc), fault cohesion (Cf), crustal cohesion (Cc), depth, fault orientation, fluid pressure, and the orientation of the greatest principle stress. Model results suggest that fault friction for the active Gwoira-Mai’iu Fault surface is 0.128≤μf≤0.265 for Cf<1.8 MPa, and 0.2≤μf≤0.265 for Cf≤0.5 MPa. Modelling of abandonment of the inactive Mai’iu Fault suggests that 0.26≤μf≤0.309 for Cf<1.8 MPa. This suggests that past slip on the inactive Mai’iu Fault, and continued slip on the active Gwoira-Mai’iu Fault, were enabled by low fault frictional strength. I also model the strength of the active Mai’iu Fault at Biniguni Falls; results suggest greater LANF friction (μf≥0.32) than the Gwoira-Mai’iu Fault surface, and inactive Mai’iu Fault. In order to explain active slip on the LANF at Biniguni Falls concurrent with widespread field observations of outcrop-scale faulting of the LANF footwall, I suggest a process whereby overall the LANF remains viable and active, but locally stress conditions exceed the LANF abandonment criteria; this results in highly localised and temporary ‘footwall damage’ where the LANF footwall is locally dissected by outcrop-scale faulting.</p>

The Geology of Eketahuna (N.Z.M.S.1. N.153)

<p>An interesting rhythmic sequence consisting of massive mudstone and groups of graded beds each about 10 ft thick is exposed near Alfredton, in the southern part of the North Island. During Opoitian time, rotation along a north-east-trending hinge line west of Alfredton caused one side of a fault block to be relatively uplifted and the other depressed, at intervals of several tens of thousands of years, while sedimentation from south-west-flowing turbidity currents was in progress. The sandy fraction of post-faulting turbidity currents were channelled along the depressed side just to the east of the submarine fault scarp, while on the middle and upper slopes of the tilted block mud was deposited from the turbidity-current clouds. As sedimentation proceeded, graded beds on-lapped eastwards up the slope of the tilted block and across the area where muds had been deposited. Later tilting of the block initiated a new rhythm.</p>

The Geology of Eketahuna (N.Z.M.S.1. N.153)

<p>An interesting rhythmic sequence consisting of massive mudstone and groups of graded beds each about 10 ft thick is exposed near Alfredton, in the southern part of the North Island. During Opoitian time, rotation along a north-east-trending hinge line west of Alfredton caused one side of a fault block to be relatively uplifted and the other depressed, at intervals of several tens of thousands of years, while sedimentation from south-west-flowing turbidity currents was in progress. The sandy fraction of post-faulting turbidity currents were channelled along the depressed side just to the east of the submarine fault scarp, while on the middle and upper slopes of the tilted block mud was deposited from the turbidity-current clouds. As sedimentation proceeded, graded beds on-lapped eastwards up the slope of the tilted block and across the area where muds had been deposited. Later tilting of the block initiated a new rhythm.</p>

Localized extension in megathrust hanging wall following great earthquakes in western Nepal

The largest (M8+) known earthquakes in the Himalaya have ruptured the upper locked section of the Main Himalayan Thrust zone, offsetting the ground surface along the Main Frontal Thrust at the range front. However, out-of-sequence active structures have received less attention. One of the most impressive examples of such faults is the active fault that generally follows the surface trace of the Main Boundary Thrust (MBT). This fault has generated a clear geomorphological signature of recent deformation in eastern and western Nepal, as well as further west in India. We focus on western Nepal, between the municipalities of Surkhet and Gorahi where this fault is well expressed. Although the fault system as a whole is accommodating contraction, across most of its length, this particular fault appears geomorphologically as a normal fault, indicating crustal extension in the hanging wall of the MHT. We focus this study on the reactivation of the MBT along the Surkhet-Gorahi segment of the surface trace of the newly named Reactivated Boundary Fault, which is ~ 120 km long. We first generate a high-resolution Digital Elevation Model from triplets of high-resolution Pleiades images and use this to map the fault scarp and its geomorphological lateral variation. For most of its length, normal motion slip is observed with a dip varying between 20° and 60° and a maximum cumulative vertical offset of 27 m. We then present evidence for recent normal faulting in a trench located in the village of Sukhetal. Radiocarbon dating of detrital charcoals sampled in the hanging wall of the fault, including the main colluvial wedge and overlying sedimentary layers, suggest that the last event occurred in the early sixteenth century. This period saw the devastating 1505 earthquake, which produced ~ 23 m of slip on the Main Frontal Thrust. Linked or not, the ruptures on the MFT and MBT happened within a short time period compared to the centuries of quiescence of the faults that followed. We suggest that episodic normal-sense activity of the MBT could be related to large earthquakes rupturing the MFT, given its proximity, the sense of motion, and the large distance that separates the MBT from the downdip end of the locked fault zone of the MHT fault system. We discuss these results and their implications for the frontal Himalayan thrust system.

A geomorphic-process-based cellular automata model of colluvial wedge morphology and stratigraphy

The development of colluvial wedges at the base of fault scarps following normal-faulting earthquakes serves as a sedimentary record of paleoearthquakes and is thus crucial in assessing seismic hazard. Although there is a large body of observations of colluvial wedge development, connecting this knowledge to the physics of sediment transport can open new frontiers in our understanding. To explore theoretical colluvial wedge evolution, we develop a cellular automata model driven by the production and disturbance (e.g. bioturbative reworking) of mobile regolith and fault scarp collapse. We consider both 90° and 60° dipping faults and allow the colluvial wedges to develop over 2,000 model years. By tracking sediment transport time, velocity, and provenance, we classify cells into analogs for the debris and wash sedimentary facies commonly described in paleoseismic studies. High values of mobile regolith production and disturbance rates produce relatively larger and more wash facies dominated wedges, whereas lower values produced relatively smaller, debris facies dominated wedges. Higher lateral collapse rates lead to more debris facies relative to wash facies. Many of the modelled colluvial wedges fully developed within 2000 model years after the earthquake with many being much faster when process rates are high. Finally, for scenarios with the same amount of vertical displacement, different size colluvial wedges developed depending on the rates of geomorphic processes and fault dip. A change in these variables, say by environmental change such as precipitation rates, could theoretically result in different colluvial wedge facies assemblages for the same characteristic earthquake rupture scenario. Finally, the stochastic nature of collapse events, when coupled with high disturbance, illustrate that multiple phases of colluvial deposition are theoretically possible for a single earthquake event.

Fault rupture in Baribis Fault possibly related to the 1847 major earthquake event in the Cirebon area

Baribis Fault is a recently identified active fault known to have thrust movement which located along the northern part of the West Java area. This E-W striking fault runs across high-populated areas, including Cirebon, Indramayu, Sumedang, and Subang area (with a probability of continuing to Jakarta and Banten areas). The last major historical earthquake occurred on November 16th, 1847 around the fault line with a radius of shaking area up to 400 km. The available high-resolution Digital Elevation Model from Geospatial Information Agency, called DEMNAS, has about 7.5-m grid data resolution but still not adequate to be used for identifying fault ruptures of this event. Hence, we conducted an Unmanned Aerial Vehicle (UAV) 3D Photogrammetry survey flown in the lower latitude (~100-m high) in the suspected sites. This study identified clear fault scarp associated with stream-valley offsets indicating strike-slip movement in the Ujung Jaya subdistrict, Sumedang. The trace of fault rupture has a 5±1-meter sinistral offset. This sharp fault deformation feature is possibly related to the 1847 earthquake in this area. This fact is different from regional morphology, which shows that the Baribis Fault is a thrust. Further study is necessary to get more detailed and precise information.