Hutt River pipeline bridge spanning across the Wellington fault

<p>This project originates from the need to provide seismic resilient solution for water supply to Wellington and Porirua. With other factors influencing the design, the pipeline crossing must withstand seismic loads including the rupture event of the Wellington Fault with movement of +/-6.5 m parallel to the river stream</p><p>The option study for the pipeline crossing concluded on using a bridge structure spanning the river and the geological Fault. This network arch bridge structure selected is provided with enough movement capacity to withstand the effects of the fault rupture movement without failure.</p><p>The length of the bridge structure is defined so to match the differential rotations between the supports to the allowable limits for the pipeline flex joints. To resist these seismic effects, the structure is provided with seismic restrainers that, at the same time as supporting the seismic load, provide enough rotation capability to accommodate movements on the foundations due to the Fault’s ruptureevent.</p>

The 2018 Mw7.5 Palu ‘supershear’ earthquake ruptures geological fault's multi-segment separated by large bends: Results from integrating field measurements, LiDAR, swath bathymetry, and seismic-reflection data

Summary On 28 September 2018, 18:02:44 local time, the Magnitude 7.5 earthquake accompanied by a tsunami and massive liquefaction devastated Palu region in Central Sulawesi, Indonesia. Comprehensive post-disaster surveys have been conducted, including field survey of surface ruptures, LiDAR, multibeam-bathymetry mapping, and seismic-reflection survey. We used these data to map fault ruptures and measure offsets accurately. In contrast to previous remote-sensing studies, suggesting that the earthquake broke an immature, hidden-unknown fault inland, our research shows that it occurred on the mappable, mature geological fault line offshore. The quake ruptured 177-km long multi-fault segments, bypassing two large releasing bends (first offshore and second inland). The rupture onset occurred at a large fault discontinuity underwater in a transition zone from regional extensional to compressional tectonic regimes. Then it propagated southward along the ∼110-km submarine fault line before reaching the west side of Palu City. Hence, its long submarine ruptures might trigger massive underwater landslides and significantly contribute to tsunami generation in Palu Bay. The rupture continued inland for another 67 km, showing predominantly left-lateral strike-slip up to 6-m, accompanied by a 5–10% dip-slip on average. The 7km sizeable releasing bend results in a pull-apart Palu basin. Numerous normal faults occur along the eastern margin. They cut the Quaternary sediments, and some of them ruptured during the 2018 event. Our fault-rupture map on mature straight geological fault lines allows the possible occurrence of early and persistent ‘supershear’, but significant asperities and barriers on segment boundaries may prohibit it.

Geochemically coupled 2D models reproduce the formation of transition zones within potash seams

&lt;p&gt;In Germany, salt deposits play an important role as industrial raw material as well as sites for energy storage. However, in geological fault zones, the contact with migrating groundwater can lead to the formation of geogenic caverns that are filled with gas and brine. These brine occurrences belong to the most significant risks in salt mining as they can cause mine flooding and land subsidence. Especially within highly soluble potash seams, the interactions between brine and salt rock result in cavernous structures surrounded by moisture penetration zones (hereinafter referred to as transition zones). In order to facilitate an early detection and a safe long-term retention of geogenic caverns, the temporal and spatial development of these transition zones was simulated.&lt;/p&gt;&lt;p&gt;In a first step, the software PHREEQC (Parkhurst &amp; Appelo, 2013) and a polytherm dataset for the hexary system Na-K-Mg-Cl-SO&lt;sub&gt;4&lt;/sub&gt;-Ca-H&lt;sub&gt;2&lt;/sub&gt;O from THEREDA were used to investigate the dissolution behavior of different potash salts. A titration model based on thermodynamic equilibrium showed that the components within a potash seam are only partly converted into secondary minerals. Brine composition and precipitations mainly depend on the ratio between kieserite and sylvite and the dissolution process only stops if water, kieserite or sylvite is fully depleted. As a consequence, 1 kg of brine can influence several tens of kilograms of potash salt. A 1D model in PHREEQC implied that the transition zone between a cavernous structure and the unaffected rock can be divided into different mineralogical regions, containing secondary minerals like glaserite, leonite or kainite besides halite. A comparison with measured data from a natural brine occurrence validates the model results. However, these models do not include temporal or spacial scaling.&lt;/p&gt;&lt;p&gt;The titration model in PHREEQC was then used as a basis for the coupling of chemistry and hydraulics which is done in Python. Transport processes free and forced convection as well as diffusion are taken into account. A 2D model of the potash seam was built considering the stratification of the rock as well as changing permeabilities due to geological fault zones and dissolution and precipitation. Cavern and transition zone are assumed to be porous media which coincides with field measurements from K+S. In the area of the dissolution front, the amount of dry potash salt that is made available for chemical reactions is controlled by a dissolution rate. Apart from that, thermodynamic equilibrium is assumed within the transition zone but a temporal scaling is still given based on the exchange rate. Besides sensitivity analyses, several scenario analyses for varying initial and boundary conditions have been done. The results are compared to a natural transition zone in a german mine and provide important insights into the long-term development of natural cavern systems within potash seams.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Parkhurst, D. L., Appelo, C. A. J. (2013): Description of input and examples for PHREEQC version 3 - a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations. US Geological Survey Techniques and Methods, 6 (A43), 497 p.&lt;/p&gt;