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Laboratory experiments on intact rock and rough fractures have demonstrated that the number and size of acoustic emission (AE) events increase and that the Gutenberg\u2010Richter <jats:italic>b<\/jats:italic>\u2010value decreases prior to coseismic failure. However, for lab fault zones of finite width, where shear occurs within gouge, the physical processes that dictate temporal variations in frequency\u2010magnitude (<jats:italic>F<\/jats:italic>\/<jats:italic>M<\/jats:italic>) statistics of lab foreshocks are unclear. Here, we report on a series of laboratory experiments to illuminate the physical processes that govern temporal variations in <jats:italic>b<\/jats:italic>\u2010value and AE size. We record AE data continuously for hundreds of lab seismic cycles and report <jats:italic>F<\/jats:italic>\/<jats:italic>M<\/jats:italic> statistics. Our foreshock catalogs include cases where <jats:italic>F<\/jats:italic>\/<jats:italic>M<\/jats:italic> data are not exponentially distributed, but we retain the concept of <jats:italic>b<\/jats:italic>\u2010value for comparison with other works. We find that <jats:italic>b<\/jats:italic>\u2010value decreases as the fault approaches failure, consistent with previous works. We also find that <jats:italic>b<\/jats:italic>\u2010value scales inversely with shear velocity and fault slip rate, suggesting that fault slip acceleration during earthquake nucleation could impact foreshock <jats:italic>F<\/jats:italic>\/<jats:italic>M<\/jats:italic> statistics. We propose that fault zone dilation and grain mobilization have a strong influence on foreshock magnitude. Fault dilation at higher shearing rates increases porosity and results in larger foreshocks and smaller <jats:italic>b<\/jats:italic>\u2010values. Our observations suggest that lab earthquakes are preceded by a preparatory nucleation phase with systematic variations in AE and fault zone properties.<\/jats:p>","DOI":"10.1029\/2021jb022175","type":"journal-article","created":{"date-parts":[[2021,11,3]],"date-time":"2021-11-03T03:12:48Z","timestamp":1635909168000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":43,"title":["Frequency\u2010Magnitude Statistics of Laboratory Foreshocks Vary With Shear Velocity, Fault Slip Rate, and Shear Stress"],"prefix":"10.1029","volume":"126","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2428-1743","authenticated-orcid":false,"given":"David C.","family":"Bolton","sequence":"first","affiliation":[{"name":"University of Texas Institute for Geophysics  Austin TX 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