Research Article| February 01, 1975 Intrusive Origin of the Matsushiro Earthquake Swarm William D. Stuart; William D. Stuart 1National Center for Earthquake Research, U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Malcolm J.S. Johnston Malcolm J.S. Johnston 1National Center for Earthquake Research, U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Geology (1975) 3 (2): 63–67. https://doi.org/10.1130/0091-7613(1975)3<63:IOOTME>2.0.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation William D. Stuart, Malcolm J.S. Johnston; Intrusive Origin of the Matsushiro Earthquake Swarm. Geology 1975;; 3 (2): 63–67. doi: https://doi.org/10.1130/0091-7613(1975)3<63:IOOTME>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Vertical and horizontal displacements, seismicity, and local magnetic field variations observed during and after the Matsushiro earthquake swarm in central Honshu, Japan, appear to be consistent with inflation of a shallow magma reservoir within a crust containing pre-existing horizontal shear stresses. Theoretical analysis shows that increased magma pressure accompanying intrusion causes a domal uplift and also reduces the pressure in adjacent rocks. Reduced pressure implies lower frictional forces on fault planes and therefore accounts for the observed diffuse seismicity and left-lateral faulting. The coseismic increase of local magnetic field intensity is in accord with the piezomagnetic effect expected during growth of a magma inclusion; the subsequent slow decrease of the field in the five years following the swarm is explained by thermal demagnetization of host rocks. Concurrent gravity changes, although comparable to estimated errors, and spring-water outflow fluctuations are compatible with both the intrusion and dilatancy fluid-flow hypotheses. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.