Frictional instabilities in clay illuminate the origin of slow earthquakes.

The shallowest regions of subduction megathrusts mainly deform aseismically, but they can sporadically host slow-slip events (SSEs) and tsunami earthquakes, thus representing a severe hazard. However, the mechanisms behind these remain enigmatic because the frictional properties of shallow subduction zones, usually rich in clay, do not allow earthquake slip according to standard friction theory. We present experimental data showing that clay-rich faults with bulk rate-strengthening behavior and null healing rate, typically associated with aseismic creep, can contemporaneously creep and nucleate SSE. Our experiments document slow ruptures occurring within thin shear zones, driven by structural and stress heterogeneities of the experimental faults. We propose that bulk rate-strengthening frictional behavior promotes long-term aseismic creep, whereas localized frictional shear allows slow rupture nucleation and quasi-dynamic propagation typical of rate-weakening behavior. Our results provide additional understanding of fault friction and illustrate the complex behavior of clay-rich faults, providing an alternative paradigm for interpretation of the spectrum of fault slip including SSEs and tsunami earthquakes.

The Role of Fabric in Frictional Properties of Phyllosilicate-Rich Tectonic Faults.

Many rock deformation experiments used to characterize the frictional properties of tectonic faults are performed on powdered fault rocks or on bare rock surfaces. These experiments have been fundamental to document the frictional properties of granular mineral phases and provide evidence for crustal faults characterized by high friction. However, they cannot entirely capture the frictional properties of faults rich in phyllosilicates. Numerous studies of natural faults have documented fluid-assisted reaction softening promoting the replacement of strong minerals with phyllosilicates that are distributed into continuous foliations. To study how these foliated fabrics influence the frictional properties of faults we have: 1) collected foliated phyllosilicate-rich rocks from natural faults; 2) cut the fault rock samples to obtain solid wafers 0.8-1.2 cm thick and 5 cm x 5 cm in area with the foliation parallel to the 5x5cm face of the wafer; 3) performed friction tests on both solid wafers sheared in their in situ geometry and powders, obtained by crushing and sieving and therefore disrupting the foliation of the same samples; 4) recovered the samples for microstructural studies from the post experiment rock samples; and 5) performed microstructural analyses via optical microscopy, scanning and transmission electron microscopy. Mechanical data show that the solid samples with well-developed foliation show significantly lower friction in comparison to their powdered equivalents. Micro- and nano-structural studies demonstrate that low friction results from sliding along the foliation surfaces composed of phyllosilicates. When the same rocks are powdered, frictional strength is high, because sliding is accommodated by fracturing, grain rotation, translation and associated dilation. Friction tests indicate that foliated fault rocks may have low friction even when phyllosilicates constitute only a small percentage of the total rock volume, implying that a significant number of crustal faults are weak.

Efficacy of repeated cycles of combination therapy for the eradication of infecting organisms in chronic bacterial prostatitis.

A total of 137 patients with a diagnosis of chronic bacterial prostatitis (CBP) were subjected to combination pharmacological therapy with antibacterial agents (ciprofloxacin/azithromycin), alpha-blockers (alfuzosin) and Serenoa repens extracts. Of those, 88 patients (64.2%) showed microbiological eradication at the completion of a 6-week cycle of therapy. Of the remaining 49 patients showing persistence of the causative organism(s) or reinfection at the end of treatment, 36 completed a second cycle of combination therapy for 6 weeks: 27 patients (75%) showed eradication of the causative organism, whereas in nine cases persistence or reinfection was observed. The cumulative eradication rate of the present study - calculated on a total of 137 enrolled patients - is 83.9%. Clinical examination showed a marked improvement of signs and symptoms linked to prostatitis. Remarkably, combination therapy could attenuate CBP symptoms prior to microbiological eradication, thus rapidly decreasing the impact of the disease on the quality of life of patients. Clinical remission was extended throughout a follow-up period of 30 months for 94% of patients, whereas seven patients showed relapse of the disease. In summary, our results indicate that about 20% of patients enrolled in this study, who were refractory to a protocol of 6-week combination therapy, could be 'rescued' by a second cycle of treatment. Clinical follow-up data show that combination therapy could ensure extended relief from CBP symptoms, and a general improvement in quality of life.