Relative motion of tectonic plates is accommodated along lithosphere-scale shear zones. The strength and stability of these shear zones control large-scale tectonics and the location of earthquakes (Bürgmann & Dresen, 2008;Molnar, 2020). Laboratory-derived strength profiles of the lithosphere postulate that the strength in the upper crust is controlled by frictional sliding along preexisting fractures, while the strength of the lower crust and upper mantle is controlled by viscous flow of rocks (Brace & Kohlstedt, 1980;Goetze & Evans, 1979;Kohlstedt et al., 1995). In this traditional view of the strength of the lithosphere, the transition from frictional sliding to viscous flow is abrupt and occurs at the intersection of Byerlee's rule with a dislocation creep flow law for a mineral of choice deforming at a constant strain rate. This sharp

Abstract:A combination of stable isotopes ( 18 O and 2 H) and hydrochemistry has been applied to investigate storage processes in relation to aquifer storage and recovery (ASR) of the shallow alluvial Quaternary aquifer in Damascus basin. The stored water, entirely taken from the Figeh springs during flood periods, was injected in a single well having a brackish groundwater. Water samples were collected from four observation wells drilled in the Damascus University Campus (DUC) site during a 3-year period (2006)(2007)(2008). The injectant water, which deviates in its chemical and isotopic signatures from that of the ambient groundwater, shows that the stored water plume remains within close proximity to the injection well (IW) (<³100 m). Thus, only two wells (W13 and W14) located at a distance less than 80 m from the injection point were affected by this injection. The observation wells located at longer distances from the IW (³145 m and ³600 m for wells W15 and WHz, respectively) were completely unaffected by the injection. Although most of the chemical and isotopic parameters usefully reflected the mixing process that occurs between the injectant water and ambient groundwater, the stable isotope ( 18 O) and chloride (Cl ) were the most sensitive parameters that quickly reflect this signature. Using a simple mass balance, the calculated proportion of injectant water reaching the well W13 was in the range of 50-90%. This proportion was even lower (30-55%) in the case of well W14. Although the drought event prevailing during this study did not much help to inject further amounts of water, higher than the injected volume (0Ð2416 M m 3 ) and also not favourable to better evaluate the fate and subsurface hydrological processes, these findings offer encouragement to continue the ASR activities, as an alternative way for better management of water resources in this basin facing intensive problems.

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&lt;p&gt;Relative motion of tectonic plates is accommodated along lithosphere-scale shear zones. The strength and stability of these shear zones control large scale tectonics and the location of earthquakes. It is widely accepted that rocks undergo a &amp;#8220;brittle-to-viscous&amp;#8221; transition as depth increases, however the details of how this transition is achieved are a topic of active research.&lt;/p&gt;&lt;p&gt;To study this transition in polymineralic rocks, we sheared bi-mineralic aggregates with varying ratio (30:70, 50:50 &amp; 70:30 vol%) of quartz (Qtz) and potassium feldspar (Kfs) at temperature, &lt;em&gt;T &lt;/em&gt;= 750&amp;#730;C and pressure, &lt;em&gt;Pc &lt;/em&gt;= 800 MPa under either constant displacement rate or constant load boundary conditions. Under constant displacement rate, samples reach high shear stress (&amp;#964; &amp;#8776; 0.4 - 1 GPa, depending on mineral ratio) and then weaken. Under constant load, the strain rate shows low sensitivity to stress below shear stresses of 400 MPa, followed by a high stress sensitivity at higher stresses irrespective of mineral ratio (stress exponent, &lt;em&gt;n&lt;/em&gt; = 9 - 13, assuming that&lt;em&gt; strain rate &amp;#8733; stress &lt;sup&gt;n&lt;/sup&gt;)&lt;/em&gt;.&lt;/p&gt;&lt;p&gt;Strain is localized along &quot;slip zones&quot; in a C and C&amp;#8217; orientation in all experiments irrespective of mineral ratio. These zones delimit larger cataclastic lenses, which develop a weak foliation. Quartz in the lenses shows pervasive Dauphin&amp;#233; twinning that leads to clear CPO patterns in the {r} and {z} rhomb planes. The {r} maxima (and {z} minima) are sub-parallel to the loading direction and rotate synthetically with increasing finite strain suggesting that they track the local &amp;#963;&lt;sub&gt;1&lt;/sub&gt; direction. The material in the slip zones shows extreme grain size reduction, no porosity and flow features. At peak strength, 1-2 vol% of the sample is composed of slip zones that are straight and short. With increasing strain, the slip zones become anastomosing and branching and occupy up to 9 vol%; this development is concomitant with strain-weakening of the sample. The best developed slip zones are observed in samples with high Kfs contents (70 &amp; 50 vol%). We infer that the material in the slip zones is formed of nanocrystalline to partly amorphous material (PAM) that is predominantly derived from Kfs. By compiling literature data on PAM development, we show that the volume of PAM increases with increasing homologous temperature and work done (stress x strain per unit volume) on the sample in rocks containing feldspars.&lt;/p&gt;&lt;p&gt;Our results suggest that strain localization leads to microstructural transformation of the rocks from a crystalline solid to an amorphous, fluid-like material in the slip zones. This material forms over a broad range of &lt;em&gt;P-T&lt;/em&gt;, stress and strain conditions suggesting that it should form readily in nature. The measured rheological response is a combination of viscous flow in the slip zones and cataclastic flow in coarser-grained lenses and can be modeled as a frictional slider coupled in parallel with a viscous dashpot.&lt;/p&gt;

Ratios of the stable isotopes (δ18O and δ2H) and deuterium excess (d-excess) values in daily and monthly composite rainwater (RW) samples collected at the Damascus area over a period of 12 years were determined to evaluate the influence of air mass trajectories on their variability. The HYSPLIT model was used for simulating the back air mass trajectories and computation of the key meteorological parameters along the trajectory path of the air masses producing single rain events. Eight major trajectory classes were distinguished for the potential rain events occurred during the studied period. The fractions of the trajectories came from the North Atlantic Ocean (AO), North Pole (NP) and the Mediterranean Sea (MS) were the highest (total ≈ 85%), whereas those of the trajectories came from the Black Sea (BS), Arabian Sea (AS) and Arabian Gulf (AG) were the lowest (each class is < 5%). The daily RW samples associated with the Siberian plateau (SP), AO, NP, MS and to some extent north Africa (NA) air masses were isotopically the most depleted (δ18O <–4‰, δ2H <–25‰, and d–excess > 10‰), whereas those coupled with the trajectories came from the BS, AS, and AG were isotopically the most enriched ​​(–2.5‰ < δ18O < − 1.0‰ and d-excess < 10‰). The findings from this study may offer new insights to better understand the effects of air mass trajectories on precipitation stable isotopes in the Eastern Mediterranean region.