Earthquakes　can　trigger　various　hydrological　responses　such　as　changes　in　groundwater　level,　tidal　response,　and　aquifer　permeability,　but　the　relationship　between　these　changes　remains　unclear.　In　this　study,　the　changes　in　groundwater　level　and　tidal　response　induced　by　the　2,008　Ms8.0　Wenchuan　earthquake,　China,　are　analyzed　for　epicenter　distances　of　tens　of　kilometers　to　more　than　1,000　km.　The　results　show　that　the　water　levels　in　34　wells　changed,　including　step-like,　pulse,　oscillation　and　gradual　changes.　The　water　levels　of　8　out　of　17　wells　with　tidal　responses　experienced　changes　in　phase　shift　based　on　tidal　analysis,　and　the　water　levels　and　phase　shifts　varied　in　opposite　directions.　The　changes　in　phase　shift　indicate　that　the　earthquake　changed　the　horizontal　or　vertical　permeability　of　the　aquifer,　or　even　the　groundwater　movement.　Several　possible　mechanisms　are　proposed　to　account　for　these　changes:　breaching　of　the　aquitard,　associated　with　five　of　the　studied　wells　in　which　phase　shift　increased　to　different　extents　but　water　level　decreased;　reduction　in　the　fracture　aperture,　accounting　for　one　well　whose　phase　shift　changed　from　positive　to　negative　but　water　level　increased;　clogging/unclogging　of　the　fractures,　associated　with　one　well　with　increasing　and　then　decreasing　phase　shift;　lower　aquifer　permeability　or　the　occurrence　of　rapid　fluctuations　in　pore　pressure,　accounting　for　another　well　where　phase　shift　gradually　decreased　but　the　water　level　changed　little.　Each　mechanism　may　deepen　understanding　of　hydrological　responses　after　earthquakes.