A diverse, cross-sectorial group of partners, stakeholders and researchers, collaborated to develop an evidence-informed Position Statement on active outdoor play for children aged 3–12 years. The Position Statement was created in response to practitioner, academic, legal, insurance and public debate, dialogue and disagreement on the relative benefits and harms of active (including risky) outdoor play. The Position Statement development process was informed by two systematic reviews, a critical appraisal of the current literature and existing position statements, engagement of research experts (N = 9) and cross-sectorial individuals/organizations (N = 17), and an extensive stakeholder consultation process (N = 1908). More than 95% of the stakeholders consulted strongly agreed or somewhat agreed with the Position Statement; 14/17 participating individuals/organizations endorsed it; and over 1000 additional individuals and organizations requested their name be listed as a supporter. The final Position Statement on Active Outdoor Play states: “Access to active play in nature and outdoors—with its risks— is essential for healthy child development. We recommend increasing children’s opportunities for self-directed play outdoors in all settings—at home, at school, in child care, the community and nature.” The full Position Statement provides context for the statement, evidence supporting it, and a series of recommendations to increase active outdoor play opportunities to promote healthy child development.

Microseismic interpretation of hydraulic fracturing requires an understanding of the mechanism of the microseismic sources. Quantitative geomechanical models can predict microseismicity for quantitative comparison with field data and can be used to reconcile 3D seismic earth models, fracture engineering, and fracture monitoring. Because microseismicity represents only one component of the geomechanical response to hydraulic fracturing, a microseismic geomechanics framework can provide insights into the connection with the fracture network. During hydraulic fracturing, microseismicity can be induced by both fluid pressure and stress mechanisms, resulting in wet events directly associated with the fracture network and remote dry events. Accurate interpretation of the hydraulic-fracture characteristics requires distinguishing identification of dry microseismicity not in hydraulic connection with the stimulated fracture network. Predictive microseismic geomechanical models also can be used to infer the primary, conductive hydraulic-fracture networks and to run scenario testing to improve engineering design.

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We use a bonded‐particle method to investigate event characteristics, b values, internal force distributions, and stress drops in triaxial deformation tests. We simulate brittle through ductile deformation regimes. We find the following: (1) Event rates are proportional to anelastic axial strain: (i) significant and accelerating events rates only occur near peak stress (brittle deformation); (ii) event rates gradually increase until the anelastic strain plateaus (ductile deformation). (2) b value patterns show a systematic decrease when approaching peak stress, after which (i) they increase again (brittle case) or (ii) reach a constant minimum (ductile case). A decrease in b values is indicative of progressive internal damage, with an increasing event rate. (3) Weak‐ and strong‐force networks exist within the sample. Macrofailure of the sample occurs due to collapse of the strong‐force network. Acoustic emissions predominantly occur (i) within the weak‐force network allowing for tensile crack opening and closing despite the large compressive external stresses, and (ii) in areas with the largest spatial force gradients, close to the strong‐force networks. All internal compressive and extensional normal forces display exponential distributions despite uniform boundary stresses. (4) Stress drops of the largest events are inversely proportional to peak stress; the largest stress drops occur for brittle failure, progressively approaching a zero magnitude for ductile deformation. The systemic correlations between b values, the number of acoustic emissions, and stress drops with the maximum principal stress may offer opportunities to invert for changes in the stress state from these remote observables during earthquake cycles.

Microseismic monitoring is increasingly being used to assess in real time the effectiveness of hydraulic fracture treatments. Operators are interested in three key questions. (1) Where are the microseismic events occurring (what is the size of the microseismic cloud)? (2) What is the failure mechanism (are fractures opening, closing, or shearing)? (3) Why is failure occurring in specific locations but not others (why are fractures not always symmetric with respect to the injection well and what is the geomechanical behavior of the reservoir)? In particular, the last question is difficult to answer from the recorded seismicity alone because the geomechanical behavior depends on the in-situ stress field, the local rock properties (lithologies), and any existing areas of weakness including faults, fractures and joints (Grob and Van der Baan, 2011). Geomechanical modeling can thus play a key role in better understanding both brittle and ductile deformation inside a reservoir because of hydraulic fracturing and the resulting microseismicity.